TECHNICAL   METHODS 


OF 


ORE    ANALYSIS 


BY 


ALBERT    H.    LOW,    B.S. 


Graduate  of  Mass.  Institute  of  Technology;  formerly  Chief  Assayer,  United  States  Mint, 

Denver;  formerly  Chief  Chemist,  Boston  and  Colorado  Smelting  Works,  Argo; 

Member  of  American  Chemical  Society;  Member  of  Society  of  Chemical  Industry; 

Member  of  Western  Association  of  Technical  Chemists  and  Metallurgists; 

Member  of  Firm  of  Von  Schulz  and  Low,  Denver;  etc.,  etc. 


SEVENTH  EDITION,  REVISED  AND  ENLARGED 

TOTAL   ISSUE,    SEVEN   THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:   CHAPMAN  &   HALL,   LIMITED 

1914 


Copyright,    1905,    1906,    1908,    1911,    1913, 

BY 
ALBERT  H.  LOW 


1,-iINj.NC-    DEPT, 


THE  SCIENTIFIC   PBE99 

•OBEHT  ORUMMOND   AND    ('OMPANV 

BROOKLYN,    N.    Y. 


Go  dfcg  Wife, 

Whose  encouragement  bas  ever  lightened  my  labor* 
This  Volume  is  Dedicated 


438545 


PREFACE  TO  THE  SEVENTH  EDITION. 


IN  this  revision  the  style  of  the  previous  editions  has  been 
adhered  to.  A  number  of  slight  corrections  and  changes  have 
been  made  throughout  the  book  and  there  are  some  additions 
and  omissions,  the  most  notable  being  in  the  chapter  on  Uranium 
and  Vanadium.  In  the  case  of  uranium  the  changes  were  very 
necessary  and  important,  as  this  element  is  now  attracting  so 
much  attention  as  a  source  of  radium. 

It  is  hoped  that  the  work  will  continue  to  be  found  worthy 
of  a  place  among  the  descriptions  of  technical  methods. 

A.  H.  Low. 
DENVER,  COLORADO,  June,  1914. 

v 


PREFACE  TO  THE   FIRST  EDITION. 


THIS  book  is  primarily  intended  as  an  aid  to  the  technical 
chemist,  but  it  is  hoped  it  may  also  prove  useful  to  the  student 
desiring  to  become  acquainted  with  technical  methods. 

It  is  a  common  experience  with  technical  chemists  to  receive 
a  sample  of  material  with  instructions  to  return  the  percentage 
of  some  constituent  whose  technical  determination  is  more  or 
less  unfamiliar  under  the  given  conditions.  In  such  a  case  the 
chemist  has  recourse  to  his  books,  and  too  frequently  is  quite 
unable  to  find  a  method  that  is  exactly  'adapted  to  the  material 
in  hand,  or  that  begins  at  the  beginning  and  tells  him  just  how 
to  proceed.  He  is  thus  left  to  work  out  his  own  salvation,  pos- 
sibly at  the  expense  of  much  valuable  time. 

In  this  book  an  attempt  has  been  made  to  supply  the  want 
thus  indicated  by  describing  methods  that  are  adapted  to  the 
cases  most  likely  to  be  met  in  practice,  although  it  is  sometimes 
practically  impossible  to  devise  a  short  technical  method  that 
will  meet  every  probable  case. 

It  has  been  my  aim  to  make  the  descriptions  so  minute  and 
complete  that  if  the  operator  will  follow  them  exactly  he  can 
scarcely  fail  to  obtain  satisfactory  results.  But  herein  lies  a  dif- 
ficulty. There  seems  to  be  a  tendency  among  technical  chemists 

vii 


viii  PREFACE  TO  THE  FIRST  EDITION. 

not  to  follow  directions  exactly.  In  carrying  out  a  method,  the 
alert  operator  sees  a  short-cut  and  takes  it,  or  a  "better  way" 
occurs  to  him  and  he  introduces  it  in  the  place  of  the  one  given. 
There  would  be  no  ultimate  harm  in  this  (since  all  methods  fall 
short  of  perfection)  if  the  operator  would  only  take  the  time  to 
investigate  and  determine  the  real  value  of  his  ideas.  In  some 
cases  he  might  discover  that  his  supposed  improvement  was 
spoiling  a  good  method,  and  he  would  come  to  agree  with  the 
author  of  the  method  who  had  himself  probably  gone  over  the 
same  ground.  I  have  seen  methods  of  my  own  thus  modified, 
and  ideas  hastily  adopted  whose  incorrectness  I  had  previously 
demonstrated  by  careful  investigation. 

I  would,  therefore,  caution  operators  to  accept  directions  as 
they  stand  until  they  have  demonstrated  the  value  of  proposed 
changes  to  a  certainty. 

Some  of  the  methods  in  the  following  collection  have  been 
devised  by  myself,  mainly  on  the  basis  of  previously  well-known 
facts,  some  are  compilations  of  the  work  of  others,  and  some 
are  modifications  of  existing  methods.  I  have  endeavored  to 
give  proper  credit  in  all  cases. 

While  I  have  aimed  at  correctness,  many  shortcomings  will 
undoubtedly  be  found,  and  I  can  only  hope  that,  such  as  it  is, 
my  work  may  prove  of  some  value  to  those  interested.  I  shall 
be  grateful  for  any  suggestions,  or  descriptions  of  improved 
methods,  to  be  incorporated  in  a  possible  future  edition. 

My  thanks   are   due  to  Dr.  W.  F.  Hillebrand    for   valuable 

information  and  suggestions. 

A.  H.  Low. 
DENVER,  COLORADO,  May,  1905. 


PREFACE  TO  THE  THIRD  EDITION. 


TECHNICAL  methods  of  ore  analysis  are  a  constant  subject 
of  study  to  the  chemists  using  them.  New  methods  are  devised 
and  old  ones  are  frequently  modified.  In  the  present  revision  I 
have  endeavored  to  make  the  work  as  up  to  date  as  possible, 
although  old  methods  are  not  always  omitted,  since  there  might 
be  cases  where  a  chemist,  through  force  of  circumstances,  would 
find  them  desirable. 

Slight  changes  are  numerous  throughout  the  book  and  much 
new  matter  has  been  added.  The  most  notable  changes  and 
additions  may  be  found  in  the  chapters  on  Aluminum,  Antimony, 
Arsenic,  Calcium,  Lead,  Magnesium,  Nickel  and  Cobalt,  Tin, 
Uranium  and  Vanadium,  Zinc,  Coal  and  Coke,  and  in  the 
Appendix. 

I  trust  those  having  occasion  to  use  the  book  will  find  it 
satisfactory  and  reliable. 

A.  H.  Low. 

DENVER,  COLORADO,  December,  1907. 


PREFACE  TO  THE  FIFTH  EDITION. 


THE  present  revision  has  been  very  thorough  and  the  im- 
portant changes  made  are  too  numerous  to  refer  to  specifically. 
Much  of  the  old  matter  has  been  modified,  rewritten,  or  entirely 
eliminated,  and  a  great  deal  that  is  new  has  been  added.  The 
previous  style  of  minute  description,  although  criticised  by  some, 
has  been  adhered  to  in  the  main.  Brief  outlines  of  methods 
might  suffice  for  many,  but  the  student  or  beginner  usually 
requires  plenty  of  detail.  Ignorance  of  some  little  detail,  or  lack 
of  attention  to  it,  is  a  frequent  source  of  trouble.  Personally,  I 
have  often  experienced  difficulty  with  a  method  that  was  new  to 
me  on  account  of  something  being  left  unsaid  in  the  description. 
With  the  opportunity  again  at  hand  to  condense,  I  decided  not  to 
do  so. 

I  beg  to  thank  those  chemists  who  have  kindly  furnished  me 
with  methods  and  information.  Their  names  will  be  found  in 
the  text. 

A.  H.  Low. 

DENVER,  COLORADO,  January,  1911. 


TABLE  OF  CONTENTS. 


CHAPTER  I. 

PAGE 


APPARATUS 


CHAPTER  II. 
ELECTROLYSIS  10 

CHAPTER   III. 
LOGARITHMS    16 

CHAPTER   IV. 

ALUMINUM      20 

CHAPTER   V. 
ANTIMONY   2j 

CHAPTER   VI. 
ARSENIC    40 

CHAPTER  VII. 
BARIUM  49 

CHAPTER  VIII. 

BISMUTH    .    52 


xii  TABLE  OF  CONTENTS. 

CHAPTER   IX. 

PAGE 

CADMIUM 61 

CHAPTER   X. 
CALCIUM 66 

CHAPTER   XL 
CHLORINE   75 

CHAPTER  XII. 
CHROMIUM  77 

CHAPTER  XIII. 
COPPER  84 

CHAPTER  XIV. 
FLUORINE 113 

CHAPTER  XV. 
IRON   119 

CHAPTER  XVI. 
LEAD 144 

CHAPTER  XVII. 
MAGNESIUM 155 

CHAPTER  XVIII. 
MANGANESE  162 

CHAPTER  XIX. 
MERCURY *79 


TABLE  OF  CONTENTS.  xiii 

CHAPTER  XX. 

PAGE 

MOLYBDENUM 185 

CHAPTER  XXL 
NICKEL  AND  COBALT 188 

CHAPTER  XXII. 
PHOSPHORUS    206 

CHAPTER  XXIII. 
POTASSIUM  AND  SODIUM 214 

CHAPTER  XXIV. 
SILICA    221 

CHAPTER  XXV. 
SULPHUR 238 

CHAPTER  XXVI. 
TIN    246 

CHAPTER  XXVII. 
TITANIUM    260 

CHAPTER  XXVIII. 
TUNGSTEN    267 

CHAPTER  XXIX. 
URANIUM  AND  VANADIUM  273 

CHAPTER  XXX. 
ZINC  284 


xiv  TABLE  OF  CONTENTS. 

CHAPTER  XXXI. 

PAGE 

COMBINING  DETERMINATIONS  303 

CHAPTER  XXXII. 
BOILER  WATER 306 

CHAPTER  XXXIII. 
COAL  AND  COKE 318 

• 
CHAPTER  XXXIV. 

TESTING  CRUDE  PETROLEUM  329 

MISCELLANEOUS 333 

TABLES 341 

INDEX 353 


TECHNICAL   METHODS   OF   ORE 
ANALYSIS. 


CHAPTER   I. 

APPARATUS. 

THE  standard  works  on  quantitative  analysis  give  descriptions 
of  the  usual  apparatus  required,  and  a  repetition  of  the  informa- 
tion is  not  contemplated  here.  I  will  simply  mention  a  few 
articles  and  arrangements  that  have  been  found  convenient  in  my 
laboratory. 

i.  Flasks. — For  most  of  my  work  I  formerly  used  a  6-oz. 
flat-bottom  flask,  ordering  a  special  form  having  a  funnel- 
shaped  mouth,  as  shown  in  Fig.  i.  The  enlarged  mouth  was 
for  convenience  in  pouring  in  weighed  material  from  the  scale- 
pan.  More  recently  I  have  preferred  an  8-oz.  flask  and  have 
found  those  manufactured  by  the  Whital  Tatum  Co.  very  suit- 
able. Their  shape  is  shown  in  Fig.  2.  Small  Erlenmeyer  flasks 
with  funnel-shaped  mouths,  as  in  Fig.  3,  are  useful  in  .special 
cases.  An  8-oz.  Erlenmeyer,  provided  with  a  lip,  is  especially 
suitable  for  the  zinc  assay.  The  lip  is  not  for  convenience  in 
pouring,  but  to  provide  an  outlet  when  the  flask  is  covered  with 
a  watch-glass.  It  prevents  the  sealing  of  the  top  with  a  con- 
tinuous ring  of  liquid,  portions  of  which  might  be  projected 
and  occasion  loss. 


TECHNICAL  METHODS  OF    ORE  ANALYSIS. 


2.  Casseroles. — Flasks  are  generally  prescribed  throughout 
this  book,  instead  of  casseroles,  for  decompositions.  They 
appear  to  be  less  liable  to  mechanical  losses  of  their  contents, 
and  for  accurate  work  are  generally  better  adapted  and  more 
convenient.  In  smelter  laboratories,  where  many  determinations 
have  to  be  made  daily,  casseroles,  in  connection  with  a  large 
hot  plate,  are  usually  preferred.  The  usual  size  is  about  3!  inches 
in  diameter.  In  many  of  the  cases  where  I  prescribe  flasks  for 


Scale  \i 


Fig.  I. 


FIG.  2. 


FIG.  3. 


decompositions  the  operator   may  employ  covered  casseroles  if 
he  prefers. 

3.  Funnels. — For  ordinary  routine  work  I  do  not  use  a  filter- 
pump  or  60°  Bunsen  funnels.  I  take  a  cheap  funnel  of  about 
the  dimensions  shown  in  the  figure  and  modify  it  as  follows: 
Cut  of!  the  stem  a  short  distance  below  the  neck  and  melt  on  a 
glass  tube  provided  with  a  loop  as  shown.  In  filtering,  the  loop 
will  cause  the  liquid  to  form  a  continuous  column  in  the  tube 
below  and  the  weight  of  this  column  will  produce  a  suction  in  the 
filter  above.  A  long  stem  will  give  a  strong  suction,  but  a  length 


APPARATUS.  3 

of  10-12  cm.  is  usually  sufficient.*  A  platinum  cone  is  not  used, 
as  the  suction  is  not  strong  enough  to  render  it  necessary.  In 
order  to  make  the  filter  fit  properly,  the  second  fold  is  made 
with  one  side  larger  than  the  other,  so  that  the  opened  filter 
will  have  an  angle  of  something  more  than  60°.  The  wet  filter 
will  then  fit  the  funnel  at  the  top  and  be  too  small  below.  This 
will  prevent  entrance  of  air  and  increase  the  filtering  surface,  so 


FIG.  4.  FIG.  5. 

that  slight  suction  will  effect  rapid  filtration.  After  the  filter  has 
been  placed  in  the  funnel,  it  is  moistened  and  the  top  pushed 
down  and  fitted  with  the  finger  until  it  is  as  air-tight  as  possible. 
Working  by  this  method,  nothing  would  be  gained  by  using  a 
funnel  having  an  angle  of  exactly  60°. 

4.  Funnel-support. — The  support  shown  in  the  figure  is  very 
convenient.  It  holds  six  funnels  in  a  compact  row,  which  facili- 
tates manipulation. 

*  These  funnels,  and  also  the  other  articles  mentioned  in  this  chapter,  are  kept 
in  stock  by  the  Denver  Fire  Clay  Co. 


TECHNICAL  METHODS  OF  ORE  ANALYSIS. 


5.  Cooling-box. — Considerable  time  can  be  saved  in  copper, 
lead,  and  other  determinations,  where  a  hot  liquid  in  a  flask  has 
to  be  cooled  to  ordinary  temperature,  by  employing  a  cooling 
box  or  tank  of  some  sort.  The  one  shown  in  Fig.  6  consists  of 
a  wooden  box  lined  with  sheet  lead  and  provided  with  pipes  for 
the  entrance  and  overflow  of  cold  water.  The  top  board,  cover- 
ing half  the  opening,  is  secured  in  place  and  has  openings  for 
the  entrance  of  6  flasks.  The  inner  end  of  each  opening  is 
enlarged  somewhat  and  the  board  is  cut  away  conically  under- 
neath, so  that  a  flask  which  will  float  will  rise  into  its  socket  and 
be  in  no  danger  of  overturning. 

n 


FIG.  6. 


FIG.  7. 


6.  Hydrogen  Sulphide  Apparatus. — Notwithstanding  all  the 
automatic  arrangements  that  have  been  devised  for  generating 
hydrogen  sulphide,  I  prefer  for  ordinary  use  in  a  small  laboratory 
the  simple  combination  shown  in  Fig.  7.  The  flask  should  be 
of  convenient  size,  say  i6-oz.,  and  the  stoppers  rubber.  The 
washing-bottle  is  about  half  filled  with  water.  It  takes  only  a 
minute  or  so  to  clean  and  charge  this  apparatus,  and  when  through 
using,  the  excess  of  gas  can  always  be  conducted  into  water  to 
keep  up  the  supply  of  hydrogen  sulphide  water.  I  have  found 
it  convenient,  in  order  to  save  hood-space,  to  arrange  the  genera- 


APPARATUS. 


tor  on  the  outside  and  connect  the  rubber  tube  with  a  glass  tube 
passing  through  the  wall. 

7.  Measuring-glass. — For  the  best  work  it  is  indispensable  that 
all  reagents  should  be  measured,  so  that  no  doubt  may  exist  as 
to  the  amount  used  for  any  purpose.  A  25-cc.  measuring-glass 
is  perhaps  the  most  convenient  size  for  constant  use.  It  seems 
to  be  an  unfortunate  fact  that  almost  all  measuring-glasses  and 
casseroles  are  made  with  the  lip  on  the  wrong  side  for  the  analyt- 
ical chemist's  use.  In  the  case  of  the  25-0:.  measuring-glass  it 
is  a  good  plan  to  have  a  glass-blower  make  a  lip  on  the  other 
side  and  also  to  attach  a  handle  of  glass  tubing  as  shown  in  Fig.  8. 
The  handle  keeps  the  fingers  from  contact  with  strong  acids, 
etc.,  which  will  inevitably  get  on  the  outside  of  the  glass. 


Scale  >3 


FIG.  8. 


FIG.  9. 


8.  Flask-holder. — The  holder  shown  in  Fig.  9  is  one  of  the 
most  useful  articles  in  my  laboratory.  My  first  holder  came 
from  Holland,  and  until  the  Denver  Fire  Clay  Co.  copied  my 
model  I  was  unable  to  obtain  a  duplicate  in  this  country.  It 
is  the  best  design  and  the  handiest  to  use  of  any  I  have  seen. 


0  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

The  portion  that  grasps  the  flask  is  lined  with  cork  cemented 
in  place  with  sealing-wax. 

9.  Apparatus  for  Standard  Solutions. — All  kinds  of  arrange- 
ments have  been  devised  for  facilitating  the  filling  of  burettes 
from    the    stock    bottles    of    standard    solutions.     Some    of  the 
methods  are  very  convenient  and  satisfactory,  but  for  the  most 
accurate  work  with  the  least  apparatus  I  prefer  the  following 
plan: 

Keep  the  standard  solutions  in  large  stock  bottles  of  about 
9  liters  capacity.     From  the  large  bottles  fill  smaller  ones,  say 

1  liter  size,  as  required.     Have  the  burettes  enlarged  to  a  funnel 
shape  at  the  top,  as  shown  in  Fig.  10,  and  keep  them  stoppered 
or  covered  with  a  cap  when  not  in  use.     When  a  burette  is  to 
be  filled  the  solution  may  easily  be  poured  in  from  the  small 
bottle.     By  this  plan  the  liquid  in  a  burette  can  always  be  mixed 
before  use  if  desired,  and  the  solution  in  the  small  bottle  also 
shaken  up.     There  are  no  stop-cocks  or  rubber  tubes  to  keep 
in  order  and  the  solution  in  the  large  bottle  is  disturbed  only 
when  necessary  to  refill  the  small  bottle. 

10.  Burette  Pinch-cock. — For  use  with  solutions  that  do  not 
attack  rubber,  I  know  of  no  better  pinch-cock  than  the  one  shown 
in  Fig.  ii.     It  consists  simply  of  a  rubber  tube  plugged  with  a 
short  section  of  glass  rod  or  a  small  bulb.     By  squeezing  the 
tube  around  the  plug  between  the  fingers  slightly,  a  channel  'is 
made  for  the  passage  of  the  liquid.     With  a  properly  propor- 
tioned tube  and  plug  the  arrangement  is  very  satisfactory. 

11.  Surface  of  Work-table. — The  most  satisfactory  surface  I 
have  tried  for  the  work-bench  is  asbestos-board,  at  least  J  of 
an  inch  thick, — \  inch  is  better.     It  should  be    cut  to   fit   the 
bench  and  laid  in  as  large  sheets  as  possible.     It  is  usually  un- 
necessary to  tack  it  in  place.     Instead  of  covering  the  entire 
bench,  it  may  suffice  to  cover  a  small  section  where  the  operator 


APPARATUS. 


does  most  of  his  work.  The  outer  edge  that  receives  wear  should 
be  painted  with  melted  paraffin, — in  fact  the  entire  surface  may 
be  thus  painted,  if  it  is  desired  to  increase  the  dura- 
bility. The  advantages  of  the  asbestos  surface  are 
its  comparative  indestructibility  under  the  action  of 
corrosive  chemicals  or  heated  articles,  its  softness, 
thus  saving  glass  utensils,  and,  if  not  painted  with 
paraffin,  its  rapid  absorption  of  spilled  liquids.  When 
much  soiled  or  worn  it  is  easily  renewed. 

Linoleum  likewise  makes   a   very  durable  and 
satisfactory  surfa  :e. 

12.  Rapid  Filtration  of  Gelatinous 
Precipitates. — Dittrich  *  has  described  \ 
a  method  for  the  rapid  nitration  of 
gelatinous  precipitates,  such  as  ferric 
or  aluminum  hydroxide,  which  consists 
in  mixing  paper  pulp  with  them  before 
filtration.  The  paper  pulp  is  prepared 
by  violently  shaking  a  piece  of  filter- 
paper  with  a  little  water  in  a  small 
stoppered  flask  or  bottle.  The  paper 
pulp  does  not  ordinarily  interfere  FIG.  10. 
with  the  subsequent  ignition  of  the  precipitate. 

I  have  found  the  scheme  very  useful  in  certain  cases.  Where 
it  is  desired  to  keep  the  volume  of  the  filtrate  as  small  as  possible, 
the  mixed  pulp  and  water  may  be  first  poured  into  the  filter  and 
the  drained-off  water  thrown  away.  The  filtration  of  the  gelat- 
inous mixture  stirs  up  the  pulp,  which  thus  appears  to  be  as 
effective  as  usual. 


FIG.  ii. 


*  Ber.,  37,  1840. 


8  TECHNICAL  METHODS  OF   ORE   ANALYSIS. 

13.  Sand-bath. —  A     "  sand-bath,"    so-called,     without    the 
sand,  supported  on  an  iron  tripod  and  heated  with  a  Bunsen 
burner,  is  an  excellent  arrangement  for  flasks  and  casseroles. 
The  bath  is  stamped  from  thin  sheet-iron  and  is  of  circular  form, 
about  5  inches  in  diameter  and  i  inch  deep.     A  piece  of  thin 
asbestos  board  placed  in  the  bath  under  a  flask,  with  a  properly 
adjusted  flame,  will  produce  a  mild  diffused  heat  for  gentle  boiling 
to  dryness,  with  the  least  liability  to  "  bumping,"  or  cracking 
the  utensil  after  dryness  is  reached.     For  a  silica  evaporation 
the  evaporating-dish  may  be  supported  on  a  scorifier  placed  in 
the  sand-bath  and  a  fairly  strong  flame  used.     This  will  effect  a 
rapid  evaporation  without  boiling,  and  the  heat  is  sufficient  for 
the  subsequent  dehydration  of  the  silica. 

14.  Boiling     Rods. — For   the   prevention   of    "bumping"    in 
boiling,  glass  rods  with  a  short  capillary  tube  on  the  lower  end 

have  been  recommended.     They  have  the. objection  that 
it  is  difficult  to  wash  out  the  capillary  opening.       To 
obviate  this  I  have  had  rods   made  with   a   cup-shaped 
cavity  in  the  end,  as  in  Fig.  12,  which  permits  of  easy 
/    \       washing.     The  larger  cavity  appears  to  serve  just  as  well 
^^      as  the  capillary  tube. 

15.  Wash-bottle  for  Ammonia,  etc. — To  prevent  the 
back-flow  of  corrosive  vapors  into  the  mouth  I  have  found  the  ar- 
rangement shown  in  Fig.  13  very  satisfactory.  The  mouth- tube  is 
of  as  large  diameter  as  convenient,  suitably  contracted  at  the  outer 
end,  and  extends  to  the  bottom  of  the  flask.  The  lower  end 
is  drawn  out  to  a  small  opening  and  is  slightly  bent  away  from 
the  exit  tube,  so  as  to  prevent  the  blown-in  air  from  entering  the 
latter.  It  is  not  bent  so  much  that  it  cannot  be  inserted  through 
the  stopper.  The  latter  is  pierced  with  a  third  hole  which  is 
covered  by  a  piece  of  sheet-rubber.  The  sheet-rubber  is  cut 
to  fit  the  top  of  the  stopper  and  is  held  in  place  by  the  tubing. 


APPARATUS.  9 

It  serves  as  a  valve  for  the  third  hole  when  manipulated  by  press- 
ing and  releasing  with  the  finger.  To  use  the  bottle,  close  the 
valve  and  blow,  taking  care  to  release  the  valve  before  discontin- 
uing the  pressure.  The  small  opening  in  the  lower  end  of  the 
mouth-tube,  together  with  the  large  diameter  of  this  tube,  will 
effectually  prevent  any  residual  pressure  from  forcing  liquid 


FIG.  13. 

back  into  the  mouth.  Do  not  have  the  small  opening  too  small, 
so  as  to  produce  very  slow  action.  The  advantage  of  the  above 
arrangement  is  its  durability,  never  getting  out  of  order. 

1 6.  Pencil  for  Glass,  etc. — For  marking  glass  and  porcelain 
the  blue  pencils  of  a  greasy  composition,  sold  for  the  purpose, 
will  be  found  most  convenient.  They  are  best  sharpened  with  a 
coarse  file. 


CHAPTER  II. 

ELECTROLYSIS. 

THE  following  remarks  on  electrolysis  are  intended  simply 
as  an  aid  to  those  who  have  to  make  an  occasional  electrolytic 
determination.  The  apparatus  necessary  for  making  a  single 
determination  of  copper,  nickel,  or  bismuth  is  described,  and  a 
few  general  directions  are  given  as  to  manipulation  and  the 
attainment  of  the  proper  conditions. 

Those  who  desire  to  pursue  the  subject  further  or  fit  up  an 
elaborate  installment  are  referred  to  the  standard  works  on 
electrochemical  analysis 

1.  Battery. — Three  J-gallon  Grenet  cells,  French  form.   These 
will    give    all  the    electromotive    force    and    current    necessary. 
Both  the  electromotive  force  and  the  current  can  be  sufficiently 
varied  by  using  from  i  to  3  cells  in  series.     The  degree  to  which 
the  zinc  plates  are  immersed  affects  the  current  but  slightly. 
The  following  solution  is  used  in  this  battery:   For  each  cell — 
water,   2    liters;   strong   sulphuric   acid    (commercial)^    200   cc.; 
powdered  potassium  dichromate,  226  grams. 

The  zinc  plates  should  be  amalgamated  with  mercury.  When 
the  battery  is  not  in  use,  it  is  best  to  remove  and  wash  the  carbons 
and  zincs  and  cover  the  jars  with  watch-glasses. 

2.  Volt- Ammeter. — Some  form  of   apparatus   for  measuring 
the  current  is  quite  necessary.      Voltmeters  and   amperemeters 


ELECTROLYSIS. 


ii 


may  be  purchased  as  separate  or  combination  instruments.  A 
form  of  the  latter,  called  the  ''Student's  Volt- Ammeter,"  manu- 
factured by  the  L.  E.  Knott  Apparatus  Co.  of  Boston,  Mass., 
will  serve  very  well  for  ordinary  work.  It  costs  about  $7. 

3.  Electrodes. — One  set  of  electrodes  is  sufficient  for  the 
determinations  mentioned  above,  as  follows:  Cathode.  A  plain 
cylinder  of  platinum  foil,  5  cm.  long  and  2.5 
cm.  in  diameter.  It  has  a  total  surface  (including 
both  sides)  of  about  78.5  sq.  cm.  and  weighs  about 
12.5  grams.  A  stout  platinum  wire  about  12  cm. 
long  is  attached  to  the  top  of  the  cylinder.  Anode. 
This  is  made  from  a  single  piece  of  stout  plati- 
num wire.  A  straight  portion  about  17  cm. 
long  rises  from  the  center  of  a  circular  base, 
made  by  coiling  the  wire  closely  about  itself,  so 
as  to  form  a  disc  about  2  cm.  in  diameter.  It 
weighs  about  8.5  grams. 

4.  Beaker  for  Electrolysis. — This  is  about  5 
cm.  in  diameter  and  9  cm.  high.     A  narrow  strip 
of  paper  is  pasted  on  the  outside  at  the  point 

indicating  a  volume  of  100  cc.  A  4-inch  watch-glass  split  in 
two  serves  as  a  cover,  the  electrode  wires  passing  through  the 
crack  in  the  center. 

5.  Supports  for  Electrodes  and   Beaker. — One  of  Classen's 
supports  with  two  clamps  (sold  by  dealers  for  about  $4)   will 
serve  very  well,  or  the  operator  can  easily  construct  a  support 
of  wood  and  a  few  binding-posts.     It  is  a  good  plan  to  have  the 
beaker  on  a  block  of  wood  or  other  elevated  support,  so  it  can 
easily  be  raised  into  place  or  lowered  away  from  the  electrodes 
as  desired.    The  elevated  arrangement  of  the  beaker  will  also 
permit  of  its  being  supported  over  a  flame  if  a  temperature  higher 
than  the  ordinary  is  required. 


FIG.  14- 
Electrodes. 


12 


TECHNICAL   METHODS    OF  ORE   ANALYSIS. 


6.  Fig.  15  shows  a  convenient  plan  for  a  single  apparatus. 
The  battery  and  volt-ammeter  are  placed  on  a  shelf  over  the 
work-bench  and  the  electrodes  are  held  by  two  binding-posts 
screwed  into  the  edge  of  the  shelf,  the  connections  being  made  as 
shown  in  the  diagram.  The  figure  is  intended  simply  to  show 
the  arrangement,  and  in  practice  the  wires  may  be  more  or  less 
concealed  and  connected  with  convenient  switches  if  desired. 
The  beaker  is  supported  on  one  or  more  wooden  blocks  resting 


FIG.  15. 

on  the  bench,  or  a  ring-stand  may  be  used.  When  an  electrolysis 
is  finished,  the  beaker  can  be  held  in  the  hand  while  the  block 
is  removed,  and  then,  with  the  current  still  passing,  it  may  be 
gradually  lowered  from  the  electrodes,  while  the  latter  are  washed 
with  a  stream  from  the  wash-bottle.  The  beaker  may  then  be 
replaced  with  one  filled  with  distilled  water  before  the  cathode  is 
disconnected.  The  volt-ammeter  indicates  amperes  to  the  right 
and  volts  to  the  left  of  a  central  zero.  The  diagram  shows  the 
ammeter  side  in  circuit,  connections  being  made  with  the  bind- 


ELECTROLYSIS.  13 

ing-posts  b  and  c  in  series,  and  the  needle  inclined  to  the  right. 
To  read  volts,  connect  the  battery  wires  directly  with  the  elec- 
trode binding-posts  and  attach  shunt  wires  from  these  posts 
to  a  and  b.  When  the  proper  connections  are  made  the  needle 
will  point  to  the  left. 

7.  Conducting  an  Electrolysis. — Clean  and  ignite  the  elec- 
trodes, and,  when  cool,  weigh  either  one  or  both  as  required. 
Now,  by  means  of  the  supports  and  binding-posts,  adjust  the 
electrodes  and  beaker  of  solution  as  follows:  Place  the  anode 
within  the  cathode  with  its  base  perhaps  a  quarter  of  an  inch 
below  the  lower  edge  of  the  cylinder.  Adjust  the  beaker  and 
volume  of  solution  so  that  the  anode  nearly  touches  the  bottom 
of  the  beaker,  and  the  top  of  the  cathode  cylinder  is  about  a 
quarter  of  an  inch  above  the  surface  of  -the  liquid.  Cover  the 
beaker  with  the  split  watch-glass  and  connect  the  electrodes 
with  the  battery.  For  copper,  nickel,  and  bismuth  the  cathode 
is  to  be  connected  with  the  zinc  pole. 

Now  include  the  ammeter  in  the  circuit  and  note  the  reading. 
It  is  not  sufficient  to  know  simply  the  amount  of  current  passing, 
since  the  actual  effect  of  this  current  in  the  solution  is  governed 
by  the  area  of  electrode  surface  over  which  it  is  distributed. 
It  is  necessary  to  have  a  certain  amount  of  current  passing  into 
a  unit  area  of  cathode  surface  in  order  to  effect  a  proper  deposi- 
tion of  metal;  in  other  words,  the  current  must  have  a  certain 
density.  100  sq.  cm.  has  been  chosen  as  the  unit  area  to  which 
to  refer  the  current  as  read  in  amperes.  Thus  if  a  current  of 
2  amperes  is  received  on  200  sq.  cm.  of  cathode,  the  current 
density  per  100  sq.  cm.  is  only  i  ampere.  Conversely,  if  i  am- 
pere of  current  is  passing  through  50  sq.  cm.  of  cathode  surface 
the  density  per  100  sq.  cm.  is  2  amperes.  The  symbol  NDioo 
is  used  to  express  the  density  of  the  current  per  100  sq0  cm.  of 
electrode  surface  exposed  to  its  action.  Knowing  the  area  of 


14  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  cathode  (including  both  sides)  actually  immersed  in  the  solu- 
tion, the  current  density  may  be  easily  calculated  from  the  read- 
ing of  the  ammeter.  Thus  if  the  ammeter  reads  2  amperes 
and  the  cathode  has  75  sq.  cm.  of  surface  immersed,  then 

2 

ND1()o= >  or  2.66  amperes. 

If  one  cell  fails  to  give  a  sufficient  current,  use  two  or  three 
in  series,  as  necessary.  Under  given  conditions  of  resistance  a 
certain  electrode  tension  is  required  in  order  to  obtain  a  stated 
strength  of  current.  This  tension  may  be  measured  with  the 
voltmeter.  The  instrument  is  not,  like  the  ammeter,  included 
in  the  main  circuit,  but  is  placed  in  a  shunt  between  the  elec- 
trodes or  points  in  the  circuit  whose  difference  of  potential  is 
to  be  measured. 

Having  attained  the  proper  current  conditions,  it  is  best  to 
leave  the  ammeter  in  the  circuit  during  the  entire  electrolysis, 
so  that  any  variation  in  the  current  may  be  noted  and  corrected 
if  necessary. 

When  the  appropriate  tests  show  the  metal  to  be  all  deposited, 
the  beaker  may  be  removed  and  the  electrodes  washed  as 
described  above,  or  according  to  the  directions  given  for  the 
metal  being  determined. 

It  is  usually  best  to  wash  the  electrode  to  be  weighed,  first 
with  distilled  water  and  then  with  strong  alcohol.  It  may  then 
be  drained  a  moment  on  filter-paper,  dried  by  holding  over  a 
hot  plate,  or  better,  in  a  drying-oven  at  about  100°  C.,  and  finally 
cooled  and  weighed. 

A  cathode  cylinder  made  of  platinum  wire  gauze  has  been 
found  to  offer  some  advantages  over  one  made  of  foil.  A  freer 
circulation  of  the  solution  is  afforded,  the  time  of  deposition 
shortened,  and  the  deposited  metal  more  firmly  adherent. 

By  the  use  of  special  apparatus  arranged  to  rapidly  rotate 


ELECTROLYSIS.  15 

one  of  the  electrodes  a  very  strong  .current  may  be  employed 
without  injuring  the  quality  of  the  deposit,  and  the  time  required 
for  a  satisfactory  electrolytic  determination  thus  shortened  to 
20  minutes  or  less.  Descriptions  of  such  methods  may  be  found 
in  recent  electrochemical  literature.* 

*  For  a  short  comprehensive  article  with  references,  see  W.  H.  Easton  in  The 
Chemical  Engineer,  Vol.   i,  p.  386.      See  also  Benner's  method,  Chap.  XIII,  12. 


CHAPTER  III. 

LOGARITHMS. 

i.  The  ordinary  calculations  of  technical  analysis  may  be 
greatly  facilitated  by  the  use  of  logarithms;  furthermore,  the 
liability  to  error  is  considerably  lessened  on  account  of  the  fewer 
figures  employed,  and  for  the  same  reason  a  calculation  is  more 
easily  checked  over  and  any  error  detected. 

When  logarithms  are  not  used  it  is  a  great  advantage  to  have 
the  standard  solutions  for  volumetric  work  of  certain  exact 
strengths,  so  that  their  factors  will  be  whole  numbers.  It  is 
frequently  difficult  to  prepare  such  solutions,  and  they  are  liable 
also  to  require  troublesome  adjustment  from  time  to  time.  By 
the  use  of  logarithms  the  necessity  for  these  hard-and-fast  stand- 
ards is  obviated,  the  calculation  with  any  factor  being  very  short. 

Tables  of  logarithms  and  antilogarithms  are  given  in  this 
book,  but  for  daily  use  it  is  best  to  have  tables  mounted  on  oppo- 
site sides  of  a  piece  of  stout  cardboard.  They  can  be  purchased 
in  this  form  of  the  Franklin  Laboratory  Supply  Co.,  15  Har- 
court  Street,  Boston,  Mass. 

For  the  benefit  of  those  who  are  unfamiliar  with  logarithms, 
or  out  of  practice,  the  following  remarks  are  appended: 

To  multiply  two  numbers,  add  their  logarithms.  The  sum 
is  the  logarithm  of  the  product. 

To  divide  one  number  by  another,  subtract  from  its  logarithm 

16 


LOGARITHMS.    •  17 

the  logarithm  of  the  divisor.  The  remainder  is  the  logarithm 
of  the  quotient. 

The  logarithm  of  a  number  is  composed  of  two  parts  —  a  posi- 
tive or  negative  integral  number  called  the  characteristic  and  a 
positive  decimal  fraction  called  the  mantissa. 

All  numbers  composed  of  the  same  figures  placed  in  the  same 
order  have  the  same  mantissa  irrespective  of  the  position  of  the 
decimal  point. 

The  characteristic  of  a  logarithm  indicates  the  position  of 
the  decimal  point  in  the  corresponding  number.  When  the 
number  has  one  significant  figure  to  the  left  of  the  decimal  point, 
the  characteristic  of  its  log.  is  o.  If  there  are  two  figures  it  is 
i,  with  three  figures  it  is  2,  etc.  A  decimal  fraction  has  a  nega- 
tive characteristic  which  is  equal  to  the  number  of  places  the 
first  significant  figure  is  removed  from  units;  thus,  the  char- 
acteristic of  the  log.  of  0.0469  is  —2;  of  the  log.  of  0.0046,  —3, 
etc.  A  negative  characteristic  is  written  with  the  minus  sign 
immediately  over  it.  It  may  be  made  positive  by  adding  10 
to  it,  the  fact  being  indicated  by  writing  10  with  a  minus  sign 
after  the  mantissa. 

The  above  rules  may  be  illustrated  as  follows: 

Number.  Logarithm. 

46  i  ....................  3-67J3 

469-1  ..................  2.6713 

46-  91  .................  1-6713" 

4.691  ................  0.6713 

.4691  ...............  1.6713  or  9.6713  —  10 

.04691  ..............  2.6713  or  8.6713  —  10 

.004691  .............  3-6713  or 


The  —10  after  the  mantissa  is  frequently  omitted  where  the 
value  of  the  characteristic  is  obvious. 


i8  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

In  many  simple  operations  the  position  of  the  decimal  point 
may  be  seen  at  a  glance  without  the  use  of  characteristics.  For 
instance,  when  working  with  a  standard  solution  where  i  cc.  = 
about  i  per  cent,  of  the  constituent  sought,  then,  if  45  cc.  have 
been  used  and  the  figure  corresponding  to  the  log.  obtained  (nc 
characteristics  having  been  used)  is  4563,  it  is  evident  that  the 
percentage  is  45.63,  and  not  4.56  or  0.45. 

Four-place  logarithm  tables  are  intended  to  be  used  with 
tumbers  of  not  more  than  four  figures.  Such  tables,  however, 
will  suffice  for  most  of  the  calculations  of  ordinary  analytical 
work. 

To  find  in  the  table  the  mantissa  of  the  log.  of  a  number  pro- 
ceed as  follows:  If  the  number  consists  of  only  i  or  2  figures, 
find  the  number  in  the  extreme  left-hand  column  and  the  man- 
tissa will  be  given  immediately  opposite  in  the  next  column  to 
the  right  headed  o.  Thus  the  mantissa  of  the  log.  of  i  or  10 
is  .coco,  of  the  log.  of  12,  .0792,  etc.  If  the  third  and  fourth 
figures  of  a  number  are  o,  the  mantissa  will  also  be  in  the  o  column 
as  before.  If  the  third  figure  is  an  integral  number,  the  mantissa 
will  be  found  in  the  same  horizontal  line,  in  the  column  headed 
with  that  figure;  thus  the  mantissa  of  the  log.  of  124  or  1240  is 
.0934.  If  the  fourth  figure  of  a  number  is  an  integral  number, 
recourse  must  be  had  to  the  column  headed  "Proportional  Parts." 
Having  found  the  mantissa  for  the  first  three  figures,  there  must 
be  added  to  it  the  amount  found  in  the  same  horizontal  line  in  the 
column  headed  with  the  fourth  figure  in  the  proportional  parts. 
Thus  the  mantissa  of  the  log.  of  1245  is  .0934  + .0017,  or  .0951. 
Having  found  a  required  mantissa,  prefix  the  characteristic 
according  to  the  rules  given  above. 

The  table  of  antilogarithms  gives  the  numbers  correspond- 
ing to  logarithms,  and  a  number  is  found  from  its  logarithm  in 
precisely  the  same  manner  as  a  logarithm  is  found  in  the  table 


LOGARITHMS. 


of  logarithms.  Thus  the  number  corresponding  to  log.  9.0974 
is  0.1251,  the  characteristic  9  signifying  the  same  as  I  and  indi- 
cating the  position  of  the  decimal  point.  In  the  same  way  log. 
1.0974  gives  12.51,  etc. 


CHAPTER  IV. 
ALUMINUM. 

i.  THE  technical  determination  of  aluminum  (usually  re- 
quired as  A12O3)  in  ores  and  metallurgical  products  is  a  some- 
what troublesome  proposition.  There  seems  to  be  no  short  and 
satisfactory  method  that  is  applicable  to  complex  substances. 
The  usual  interfering  elements  are  iron,  manganese,  arsenic, 
antimony  and  phosphorus.  Chromium  and  titanium  would 
prove  sources  of  trouble,  but  are  so  rarely  present  in  western 
lead- smelting  ores  that  they  may  ordinarily  be  neglected.  There 
are  two  general  methods  of  procedure,  the  direct  and  the  indirect. 
In  the  direct  method  the  aluminum  is  weighed  as  A1PO4  or 
A12O3.  In  the  indirect  method  the  aluminum,  iron,  and  per- 
haps phosphorus  are  weighed  together  as  A^Os,  Fe2Os  and 
P2C>5,  the  latter,  of  course,  combined  to  form  a  phosphate  with 
the  others.  The  alumina  is  then  found  by  difference  after 
determining  and  deducting  the  weight  of  the  other  constituents 
of  the  mixture. 

2.  Direct  Method. — Treat  0.5  gram  of  the  ore  in  a  plati- 
num dish  with  2-3  cc.  of  strong  sulphuric  acid  and  about  20  cc. 
of  strong  pure  hydrofluoric  acid.  Evaporate  over  a  water- bath 
or  other  gentle  heat  as  far  as  possible  and  then  cautiously  raise 
the  heat  until  'the  sulphuric  acid  is  fuming  copiously.  Allow 
to  cool,  add  water  and  a  little  hydrochloric  acid  and  warm  the 


ALUMINUM.  21 

mixture  until  the  dish  is  free  from  adhering  insoluble  matter. 
Now  transfer,  using  as  little  wash-water  as  possible,  to  an  8-oz. 
flask.  Add  6  grams  of  potassium  sulphate,  5  cc.  of  strong  sul- 
phuric acid  and  one-eighth  of  a  9-cm.  filter.  Boil  the  mixture 
gently  at  first,  to  expel  water  and  hydrochloric  acid,  then,  as  the 
sulphuric  acid  begins  to  fume,  the  heat  may  be  increased  as 
strongly  as  the  prevention  of  undue  foaming  will  permit,  finally 
with  the  flask  in  a  holder,  over  a  free  Bunsen  flame,  until  any 
free  sulphur  is  entirely  expelled  and  the  separated  carbon  is 
completely  oxidized,  .leaving  a  clean  mass  or  melt  with  but  little 
free  sulphuric  acid.  Allow  the  flask  to  cool  in  an  inclined  position 
to  avoid  cracking.  The  object  of  the  filter  paper  is  to  reduce 
any  arsenic  or  antimony  to  the  ous  condition,  and  thus  render 
its  subsequent  precipitation  as  sulphide  rapid  and  complete. 

3.  After  cooling,  add  150  cc.  of  water  and  5  cc.  of  strong 
hydrochloric  acid  and  warm  the  mixture  until  everything  soluble 
has  dissolved.  If  a  trifling  residue  remains  it  may  usually  be 
neglected.  From  a  larger  residue,  decant  most  of  the  solution 
through  a  filter  and  heat  the  residue  with  dilute  hydrochloric 
acid,  repeating  these  operations  once  or  twice  if  necessary. 
Calcium  sulphate  or  lead  salts  may  thus  be  dissolved  or  greatly 
reduced  in  amount.  Pour  the  solutions  through  the  filter, 
finally  transferring  any  remaining  residue,  and  wash  with  hot 
water.  Reserve  the  filtrate.  The  final  residue  may  consist  of 
a  little  barium  or  calcium  sulphate  or  other  unimportant  sub- 
stance. If  its  character  is  thus  recognized  it  may  be  negletced, 
but  if  this  is  uncertain  and  aluminum  is  liable  to  be  present  it  is 
best  to  treat  it  further.  Ignite  filter  and  contents  in  a  platinum 
dish  until  the  carbon  is  consumed.  The  residue  may  now  be 
either  again  evaporated  with  a  little  hydrofluoric  and  sulphuric 
acid  nearly  to  dryness,  or,  if  silica  is  apparently  absent,  fused  with 
a  little  mixed  sodium  and  potassium  carbonates.  In  either  case 


22  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  solution  of  the  product,  acidified  with  hydrochloric  acid, 
may  be  added  directly  to  the  reserved  filtrate,  without  regarding 
any  residue  of  barium  sulphate. 

4.  The  liquid  is  now  an  acid  solution  of  the  various  bases. 
It  should  not  be  too  acid,  and  it  is  therefore  safer  to  nearly 
neutralize  with  ammonia  and  then  reacidify  with  an  excess  of 
5  cc.  of  hydrochloric  acid.     Now  dilute  to  about  300  cc.  with 
hot   water  and   pass   in  hydrogen  sulphide   to   precipitate   the 
metals  of  that  group.     Ten  minutes  will  usually  suffice  for  this 
precipitation,  since  any  arsenic  or  antimony  is  in  the  ous  con- 
dition and   will  come  down  quickly.     It  is  well,  however,  to 
have  the  liquid  fairly  cool  at  the  end,  to  ensure  the  complete 
precipitation  of  any  lead.     Filter,  washing  with  water  contain- 
ing  hydrogen    sulphide.     Boil   the   filtrate    until   all   hydrogen 
sulphide  is  expelled  and  then  oxidize  the  iron  to  the  ferric  con- 
dition by  the  cautious  addition  of  a  few  cubic  ccnt'.rre  ers  of  nitric 
acid  to  the  boiling  solution.    Now  dilute  to  abou '.  400  cc.  with  cold 
water  and  allow  to  cool  to  room  temperature.    The  liquid  is  now 
ready  for  the  precipitation  of  the  aluminum  as  phosphate  aciord- 
ing  to  Peters's  modification  of  W6h!er's  method,*  as  follows: 

5.  Add  ammonia  until  the  soli:ticn  becomes  brown  or  dark 
red  in  color,   according  to  the  amount  of  iron  present,  but  still 
contains  no  precipitate.    Now  add  3.3  cc.  of  hydrochloric  acid 
of  1.2  sp.  gr.  and  2  grams  of  sodium  phosphate  dissolved  in 
water  and  filtered  if  necessary.     Stir  until  any  precipitate  formed 
is  dissolved  and  the  solution  becomes  perfectly  clear  again. f 
Now  add  10  grams  of  sodium  thiosulphate,  dissolved  in  water 

*  Blair,  Chem.  Anal,  of  Iron,  3rd  ed.,  p.  250. 

t  Blair's  directions.  Personally,  I  have  frequently  found  the  solution  to 
become  more  and  more  turbid.  I  then  cautiously  add  more  hydrochloric  acid 
until  the  solution  clears,  note  the  extra  amount  used  and  increase  the  sodium 
thiosulphate  at  the  rate  of  10  grams  for  each  3  cc.  of  acid  required. 


ALUMINUM.  23 

(and  filtered  if  necessary),  and  15  cc.  of  acetic  acid  of  1.04  sp.  gr. 
(This  strength  may  be  approximated  by  adding  10  cc.  of  water  to 
5  cc.  of  the  80  per  cent,  acid.)  Heat  to  boiling,  boil  15  minutes,* 
and  filter  as  rapidly  as  possible  on  an  ashless  filter.  Wash 
thoroughly  with  hot  water.  If  the  amount  of  the  precipitate 
is  small  it  may  at  once  be  dried,  ignited  in  a  porcelain  crucible, 
together  with  the  filter,  and  weighed  as  A1PC>4.  Multiply  this 
weight  by  0.4185  to  obtain  the  weight  of  the  A^Oa. 

If  the  precipitate  is  large  in  amount  it  should  be  redissolved 
and  reprecipitated.  Rinse  it  into  a  beaker,  add  a  little  hydro- 
chloric acid  to  dissolve  it,  and  then  pour  through  the  filter,  to 
dissolve  what  was  not  rinsed  off,  and  wash  the  filter  thoroughly. 
Dilute  the  filtrate  somewhat,  if  necessary,  add  ammonia  in  slight 
excess,  and  then  reacidify  with  acetic  acid  in  slight  excess.  Heat 
to  boiling,  filter,  and  wash  with  hot  water.  Then  dry  (I  have 
found  this  apparently  unnecessary),  ignite,  and  weigh  as  above 
described.  It  is  always  well  to  again  boil  the  filtrate  from  the 
first  precipitate  of  aluminum  phosphate  for  some  time  and  filter 
off  the  precipitate  formed  on  a  separate  filter.  Ignite  this  in 
a  separate  crucible  (not  weighed),  and  if  any  A1PO4  is  found, 
brush  it  in  with  the  main  portion.  A  precipitate  of  sulphur 
will  thus  always  be  obtained  and  the  presence  of  aluminum 
phosphate  can  be  determined  only  by  igniting  it.  It  is  best  to 
repeat  this  boiling  and  filtering  until  the  ignited  precipitate 
leaves  no  residue. 

6.  Method  of  J.  M.  Bonsai. — This  scheme,  which  employs  a 
modification  of  Wohler's  method,  is  described  as  follows  (Pardoe's 
revision  of  Furman's  " Manual  of  Practical  Assaying,"  p.  218): 
Weigh  out  0.5  gram  of  the  finely  powdered  ore  and  mix  with 
three  to  five  times  its  weight  of  the  mixed  carbonates  of  sodium 

*  Blair's  directions.     I  have  found  thirty  minutes  safer. 


24  TECHNICAL   METHOD    OF  ORE   ANALYSIS. 

and  potassium  in  a  platinum  crucible.  Fuse  until  the  melt  is 
clear.  Dissolve  the  fused  mass  in  hot  water  and  hydrochloric 
acid,  digesting  if  necessary.  Evaporate  to  dryness  and  remove 
silica  in  the  usual  way  (xxiv,  n).  Add  to  the  nitrate  from 
the  silica  20  grams  of  ammonium  chloride,  roughly  weighed,  and 
precipitate  the  iron  and  aluminum  with  ammonia.  Filter  the 
precipitated  hydroxides  and  wash  with  hot  water  until  chlorine 
is  removed  (shown  by  adding  silver  nitrate  to  portions  of  the 
nitrate,  a  white  precipitate  of  silver  chloride  being  formed). 
Remove  the  precipitate,  which  consists  of  A^Os,  Fe2Os,  and 
Cr2O3  (if  chromium  is  present),  from  the  filter  and  dissolve 
in  as  small  a  quantity  of  dilute  hydrochloric  acid  (one  part  HC1, 
sp.  gr.  i. 20,  and  one  part  H^O)  as  possible.  It  is  very  important 
at  this  point  to  avoid  an  excess  of  hydrochloric  acid.  Now  add 
to  the  solution  about  5  cc.  of  a  saturated  solution  of  hydrogen 
sodium  phosphate  until  a  slight  precipitate  appears,  and  then 
2  or  3  drops  of  hydrochloric  acid,  or  sufficient  to  clear  up  the 
solution.  Now  add  30  grams  of  ammonium  chloride,  roughly 
weighed,  and  15  cc.  of  a  saturated  solution  of  sodium  thiosulphate 
and  boil  for  fifteen  minutes.  Filter  on  an  ashless  filter,  wash  five 
or  six  times  with  boiling  water,  dry,  place  in  a  porcelain  crucible 
and  ignite,  gently  at  first,  until  all  carbon  has  been  burned  off, 
as  the  aluminum  phosphate  may  fuse  and  render  the  combustion 
difficult.  Weigh  as  A1PO4,  multiplying  by  0.4185,  to  obtain 
the  weight  of  the  A12O3. 

7.  Note  on  the  Above. — The  decomposition,  as  described,  is 
not  applicable  to  sulphides  or  material  containing  easily  reducible 
metals.  In  such  cases,  or  where  in  doubt,  I  would  suggest  the 
following  procedure:  Treat  0.5  gram  of  the  ore  in  an  8-oz.  flask 
(or  small  covered  casserole)  with  whatever  acids  are  necessary 
for  its  decomposition.  Usually  10  cc.  of  strong  hydrochloric 
acid,  subsequently  followed  with  5  cc.  of  strong  nitric  acid  if 


ALUMINUM.  25 

sulphides  are  present,  will  prove  sufficient.  Finally,  add  5  cc. 
of  strong  sulphuric  acid  and  boil  to  fumes.  Now,  manipulating 
the  flask  over  a  free  flame,  expel  nearly  all  the  remaining  sulphuric 
acid.  Cool,  add  30  cc.  of  water,  heat  to  boiling,  and  allow  to 
stand,  hot,  until  any  anhydrous  ferric  sulphate  is  entirely  dis- 
solved. Then  cool  to  room  temperature  or  cooler  and  filter 
through  a  p-cm.  filter,  washing  the  residue  four  times  with  dilute 
(i :  10)  sulphuric  acid.  Receive  the  filtrate  in  an  evaporating- 
dish.  Add  ammonia  in  slight  excess  to  neutralize  the  sulphuric 
acid,  then  reacidify  slightly  with  hydrochloric  acid  and  place 
the  solution  to  evaporate  to  dryness.  Wash  the  residue  on  the 
filter  with  hot  dilute  hydrochloric  acid,  containing  some  ammonium 
chloride,  until  any  lead  sulphate  is  removed,  then  ignite  filter 
and  residue  in  a  platinum  crucible  or  dish  until  the  carbon  is  all 
consumed.  Finally,  fuse  the  residue  with  the  mixed  carbonates, 
as  described  above,  and  add  the  acidified  solution  of  the  melt  to 
the  portion  already  evaporating,  proceeding  from  this  point  as 
described. 

I  would  also  suggest  washing  the  precipitated  aluminum 
phosphate  at  least  ten  times,  to  insure  the  removal  of  all  soluble 
salts. 

8.  Indirect  Method. — This  is  useful  in  technical  work  only 
when  the  precipitate  of  mixed  iron  and  aluminum  hydroxides 
can  be  easily  obtained  free,  or  nearly  so,  from  phosphorus  and 
arsenic,  as  in  the  case  of  clay  and  similar  material.  If  phosphorus 
or  arsenic  are  liable  to  be  present  in  more  than' negligible  amount 
their  separation  or  estimation  is  involved,  and  the  process  usually 
becomes  too  tedious  for  a  technical  method.  Where  the  method 
is  applicable  the  procedure  may  be  as  follows: 

Take  0.5  gram  of  the  substance  and  decompose  it,  according 
to  its  nature,  either  with  acids  or  by  fusion  in  platinum  with  a 
mixture  of  3  grams  of  sodium  carbonate  and  2  grams  of  potassium 


26  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

carbonate.     In  the  latter  case  fuse  until  clear,  disintegrate  the 
cold  melt  by  heating  with  water  and  transfer  the  mixture  to  an 
evaporating-dish.     Cover  the  dish,  acidify  with  hydrochloric  acid' 
and  evaporate  to  dryness  to  remove  silica.     If  acids  alone  have 
sufficed   for  the  decomposition,   the  solution  may  be  similarly 
evaporated.     Sometimes  an  evaporation  to  dryness,  in  platinum, 
with  hydrofluoric  acid  mixed  with  hydrochloric  or  a  little  sulphuric 
acid  (moistening  the  material  with  the  latter  before  adding  the 
hydrofluoric  acid)  may  serve  to  decompose  the  substance  and 
remove  silica  at  the  same  time.     After  the  evaporation  take  up 
in  hydrochloric  acid  and  dilute.     Dilute  the  filtrate  from  the 
silica,   or  the  solution  otherwise  obtained  free  from  silica,   to 
from  100  to  300  cc.,  according  to  the  amount  of  iron  or  aluminum 
apparently  present,  make  slightly  alkaline  with  ammonia  and 
heat  to  boiling.     Keep  at  a  boiling  temperature  for  a  short  time, 
then  remove  from  the  heat  and  allow  to.  settle  somewhat  and 
filter,  washing  with  hot  water.     If  the  amount  of  the  precipitate 
is  large  it  is  best  to  redissolve  it  in  hydrochloric  acid  and  repeat 
the  precipitation.     It  is  always  safer  to  do  this  in  any  case. 
The  final  washing  should  be  very  thorough,  10  to  20  times  with 
hot  water,  or  until  a  portion  of  the  filtrate  shows  no  test  for 
chlorine.      Finally,   dry  and  ignite  the  mixed  hydroxides  and 
weigh  as  Fe2O3  and  A12O3.     After  weighing,  fuse  in  platinum 
with  a  little  potassium  acid  sulphate,  take  up  the  melt  in  dilute 
hydrochloric  acid  and  determine  the  amount  of  Fe^Os  volumet- 
rically,  thus  arriving  at  the  weight  of  the  A12O3  by  difference. 
Phosphorus,  arsenic,  and  the  heavy  metals  are  presumably  absent 
from  the  substance  tested.     If  manganese  is  present  in  appre- 
ciable amount  it  should  be  separated  from  the  iron  and  aluminum 
by  the  basic  acetate  method  (see  Fresenius  or  Treadwell)  previous 
to  the  precipitation  by  ammonia. 


CHAPTER   V. 

ANTIMONY. 

THE  technical  determination  of  antimony  in  ores,  etc.,  is 
best  made  by  volumetric  methods.  The  most  troublesome 
interfering  element  is  usually  arsenic.  Where  arsenic  is  known 
to  be  absent  or  negligible  the  procedure  in  the  following  method 
may  be  shortened  by  omitting  the  operations  for  its  removal. 

1.  Before   beginning   treatment   the   nature   of   the   material 
should   be   considered.     Most   sulphides   and   mixed   ores   yield 
readily  to  the  acid  treatment  described  below,  but  oxidized  ores 
rich  in   antimony  may   fail   of  complete  decomposition.     Such 
material  is  easily  decomposed  by  the  method  described  in  6. 

2.  Method  Applicable  to  Sulphides  and  Most  Mixed  Ores  and 
Low-Grade    Oxides.*  —  Take  0.5  gram  of  the  finely  pulverized 
ore  in  an  8-oz.  flask,  add  5  grams  of  ammonium  sulphate,  i  gram 
of  potassium  sulphate,  10  cc.  of  strong  sulphuric  acid  and  one- 
eighth  of  a  Q-cm.  filter.     The  object  of  the  latter  is  to  provide 
organic  matter  for  the  reduction  of  arsenic  and  antimony  to  the 
ous  condition,  thus  facilitating  the  solution  of  the  antimony  and 
also  rendering  the  subsequent  precipitation  of  both  metals  as 
sulphides  rapid  and  complete.     Heat  the  mixture  cautiously  at 
first,  over  a  small  free  flame,  then  increase  the  heat  gradually, 
and  finally  manipulate  the  flask  in  a  holder  over  the  full  flame  of 
a  Bunsen  burner.    Continue  until  any  free  sulphur  is  all  expelled, 
the  separated  carbon  completely  oxidized  and  the  free  sulphuric 
acid  almost  entirely  driven  off.  leaving  a  clean  melt  from  which 

*  A.  H.  Low,  Jour.  Am.  Chem.  Soc.,  XXVIII,  1715,  modified. 

27 


28  TECHNICAL   METHODS   OF   ORE   ANALYSIS. 

ammonium  sulphate  is  slowly  volatilizing.  If  not  perfectly  fluid 
add  sufficient  potassium  acid  sulphate  to  make  it  so.  The  above 
treatment  may  appear  severe  for  a  flask,  but  one  rarely  breaks, 
although,  at  the  end,  the  bottom  is  apparently  almost  at  low 
redness.  Allow  the  melt  to  cool  with  the  flask  on  its  side,  as  other- 
wise the  solidifying  cake  may  crack  it,  or  spread  the  melt  around 
on  the  sides  while  cooling. 

3.  After  cooling,  add  25  cc.  of  water,  25  cc.  of  strong  hydro- 
chloric acid  and  2  or  3  grams  of  tartaric  acid.     Cover  the  flask 
with  a  small  watch-glass  and  warm  the  mixture,  but  do  not  heat 
to  boiling  lest  some  arsenic  be  lost  by  volatilization,  in  case  it  is 
to  be  determined.     Boiling  would  also  weaken  the  acid  strength. 
Maintain  fairly  hot,  with  occasional  agitation,  until  solution  is 
as  complete  as  possible.     Anhydrous  ferric  sulphate  will  dissolve 
more  quickly  if  a  little  ferrous  sulphate  be  added.     Now  rinse 
off  the  watch-glass  with   a  very   little  water,  add   25  cc.  more 
of  cold  strong  hydrochloric  acid  and   then   pass    in    hydrogen 
sulphide   until   any   arsenic   present   is   completely   precipitated. 
As  the  arsenic  is  in  the  ous  condition  this  will  take  only  a  short 
time,  perhaps  ten  minutes.     Some  copper  may  be  precipitated, 
but  no  antimony  or  tin.     Filter  through  a  double  Q-cm.  filter 
that  has  been  moistened  with  2 :  i   hydrochloric  acid.     Use  an 
ordinary  suction  funnel.     A  platinum  cone  will  insure  the  filter 
from  breaking.      Rinse  off  the  delivery-tube  with   2 :  i    hydro- 
chloric acid  and  remove  it.     Rinse  out  the  flask  several  times 
with  the  same  acid  mixture,  and  wash  the  precipitate  with  it 
also  at  least  six  times.     Receive  the  filtrate  in  a  large  beaker. 
If  arsenic  is  to  be  determined,  reserve  the  precipitate,  and  any 
particles  adhering  to  the  flask  and  delivery-tube,  to  be  proceeded 
with  according  to  vi,  2.     Continue  with  the  antimony  as  follows: 

4.  Dilute  the  filtrate  with  double  its  volume  of  warm  water 
and  saturate  it  with  hydrogen  sulphide.     Simple  dilution  will 


ANTIMONY.  29 

cause  a  precipitation  of  antimony  sulphide,  but  it  is  not  safe  to 
omit  passing  the  gas  also.  Filter  off  the  precipitate,  which  may 
consist  of  antimony  sulphide  mixed  with  other  sulphides,  and 
wash  it  from  six  to  ten  times  with  hydrogen  sulphide  water  so  as 
to  remove  nearly  all  the  chlorides.  Use  an  n-cm.  filter.  With 
a  jet  of  hot  water,  using  as  little  as  possible,  wash  most  of  the 
sulphide  from  the  filter  into  a  beaker.  Add  a  little  colorless 
sodium  sulphide  solution  *  and  warm  to  effect  the  solution  of 
the  antimony  sulphide.  Pour  through  the  last  filter  and  wash 
filter  and  residue  well  with  hot  water  containing  a  little  sodium 
sulphide.  One  extraction  will  usually  suffice.  Receive  the 
filtrate  in  an  8-oz.  flask.  Small  amounts  of  antimony  sulphide 
may  be  dissolved  directly  on  the  filter.  To  the  filtrate  add 
2  grams  of  potassium  sulphate  and  about  8  cc.  of  strong  sulphuric 
acid.  (The  addition  of  organic  matter  for  reduction  is  here' 
unnecessary.)  Boil  as  previously  described  (2)  to  expel,  first 
the  water,  then  all  the  free  sulphur,  and  finally  most  of  the  free 
acid.  Small  amounts  of  chlorine  appear  to  be  harmlessly  expelled 
before  the  antimony  sulphide  is  decomposed.  Cool  with  flask 
inclined.  Add  to  the  residue  50  cc.  of  hot  water  and  10  cc.  of 
strong  hydrochloric  acid.  Heat  to  effect  solution  and  then  boil 
for  a  short  time  to  expel  any  possible  sulphur  dioxide.  Finally, 
add  10  cc.  more  of  strong  hydrochloric  acid,  cool  under  the  tap, 
dilute  to  about  140  cc.  with  cold  water  and  titrate  to  the  usual 
pink  tinge  with  a  standard  solution  of  potassium  permanganate. 
The  solution  ordinarily  used  for  iron  titrations  (2.83  grams 
per  liter)  will  answer.  The  iron  value  of  the  permanganate 

*  Dissolve  100  grams  of  sodium  hydroxide  in  sufficient  water  and  dilute  the 
solution  to  i  liter.  Saturate  600  cc.  with  hydrogen  sulphide  and  then  add  the 
remaining  400  cc.  5  or  6  cc.  usually  suffice  for  the  above  extraction.  Ammo- 
nium sulphide  may  be  used,  although  it  dissolves  more  copper  sulphide.  A 
small  amount  of  chlorides  in  the  reagents  will  not  cause  an  appreciable  subse- 
quent loss  of  antimony  by  volatilization. 


30  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

multiplied  by  1.075,  or>  tne  oxalic  acid  (C2O4H2-2H2O)  value 
multiplied  by  0.9532,  will  give  the  antimony  value.  A  small 
amount  of  copper  (frequently  present)  has  no  influence  on  the 
titration.  If  the  solution  becomes  turbid  before  or  during  the 
titration,  add  a  few  grams  of  tartaric  acid  to  clarify  it. 

5.  Notes. — The  mixture  of  sulphates  used  in  the  decom- 
position is  better  than  potassium  sulphate  alone.  The  ammonium 
sulphate,  by  slowly  volatilizing,  prevents  the  temperature  from 
getting  too  high  during  the  oxidation  of  the  carbon,  and  the 
small  quantity  of  potassium  sulphate  added  is  to  insure  that  no 
antimony  or  arsenic  shall  volatilize  as  an  ammonium  salt.  With 
potassium  sulphate  alone  the  temperature  may  become  so  high 
before  all  the  carbon  is  oxidized  as  to  effect  a  slight  reduction 
of  antimony  or  arsenic  to  metal,  which  may  be  lost  by  volatiliza- 
tion. 

Sometimes  an  appreciable  amount  of  undecomposed  material 
remains  after  the  above  acid  treatment  of  the  substance.  If  this 
is  likely  to  contain  antimony  it  may  be  further  treated  as  follows: 
Proceed  as  described  until  after  the  first  filtration,  thus  obtaining 
the  undecomposed  residue  and  any  arsenic  sulphide  on  the  filter. 
Reserve  the  filtrate  and  continue  with  the  material  on  the  filter 
as  described  for  arsenic  (vi,  2),  until  the  latter  is  removed, 
omitting  this  step,  of  course,  if  no  arsenic  is  present.  Ignite 
the  thoroughly  washed  filter  and  residue  at  a  low  temperature 
in  the  thin  iron  crucible  described  below  (6)  until  the  carbon  is 
all  burned  off,  and  then  fuse  with  a  little  sodium  hydroxide. 
Dissolve  the  melt  in  hot  water,  transfer  to  a  beaker,  acidify  with 
hydrochloric  acid,  and  add  the  solution  to  the  reserved  filtrate. 
Continue  with  this  as  described. 

Tin  is  without  influence  on  the  antimony  result  (since  it 
exists  in  the  final  solution  as  stannic  sulphate)  but  may  prove  a 
great  annoyance,  if  much  is  present,  owing  to  its  troublesome 


ANTIMONY.  31 

sulphide.  In  such  a  case  I  have  found  Clark's  oxalic  acid  method 
for  preventing  the  precipitation  of  tin  sulphide  very  satisfactory. 
Simply  dissolve  10  grams  of  oxalic  acid  crystals  in  the  nitrate 
containing  the  antimony,  previous  to  diluting  and  passing  in 
hydrogen  sulphide.  The  tin  will  be  kept  in  solution  and  occasion 
no  further  trouble. 

6.  Decomposition  of  Oxidized  Material. — In  a  thin-spun  iron 
crucible  of  about  60  cc.  capacity  melt  about  8  grams  of  sodium 
hydroxide.  (I  take  about  three  inches  of  the  stick  hydroxide, 
broken  into  short  pieces.)  Heat  until  the  moisture  is  expelled 
and  quiet  fusion  attained  and  then  allow  to  cool.  It  is  a  good 
plan  to  add  a  very  small  pinch  of  potassium  nitrate  to  the  melt 
just  previous  to  cooling  to  guard  against  any  subsequent  reduc- 
tion of  metal  from  the  ore.  Weigh  0.5  gram  of  the  ore,  transfer 
it  to  the  prepared  crucible,  cover  with  a  loosely-fitting  porcelain 
cover  and  fuse  the  mixture.  Heat  very  cautiously  at  first  until 
violent  bubbling  has  ceased,  and  then  with  the  full  flame  of  a 
Bunsen  burner  until  quiet  fusion  is  attained.  Remove  the  cover 
and  pour  the  melt  into  a  clean  metallic  dish  floating  in  a  beaker 
of  water.  I  use  a  2-|-inch  nickel  dish.  It  is  best  to  cover  the 
hot  cake  with  a  small  porcelain  crucible  cover  dropping  within 
the  dish,  to  prevent  mechancial  loss  in  case  the  cake  cracks  and 
flies  apart  violently.  Place  a  little  cold  water  in  a  5^-inch 
casserole  and  set  the  hot  crucible  therein;  then  turn  the  latter 
on  its  side  so  as  to  admit  the  water  and  heat  to  boiling.  Move 
the  crucible  about  with  a  glass  rod,  and  when  the  outside  is 
clean  wash  it  off  so  as  to  remove  the  crucible  with  the  fingers. 
The  inside  of  the  crucible  may  still  contain  some  of  the  undis- 
solved  melt.  Pour  in  a  little  water,  acidify  with  hydrochloric 
acid,  and  bring  the  dilute  acid,  by  means  of  a  glass  rod,  in  contact 
with  any  adhering  melt.  When  all  is  dissolved,  wash  the  solution 
Into  the  casserole.  Now  add  the  detached  cake  and  the.  crucible 


32  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

cover  with  the  top  (provided  with  a  loop)  up.  Cover  the  casserole 
and  add  about  30  cc.  of  strong  hydrochloric  acid,  which  should 
prove  an  ample  excess.  Heat  to  boiling  and  the  cake  will 
quickly  dissolve.  Now  remove  and  wash  off  the  watch-glass, 
and  by  means  of  a  bent  wire  lift  out  the  crucible  cover  and  wash 
it.  As  a  rule  the  decomposition  is  perfect  and  everything  goes 
into  solution  in  the  hydrochloric  acid,  even  the  silicic  acid.  If 
scales  of  oxide  from  the  crucible  remain,  allow  to  settle,  decant 
the  solution  and  warm  the  residue  with  a  little  strong  hydro- 
chloric acid,  adding  also,  if  necessary,  a  few  crystals  of  potassium 
chlorate.  Add  the  solution  to  the  main  portion.  Barium  might 
separate  as  sulphate,  but  this  is  easily  distinguishable  from 
undecomposed  ore.  Now  add  2  or  3  grams  of  tartaric  acid,  and 
when  it  has  dissolved  dilute  sufficiently  and  filter  if  necessary, 
which  is  rarely  the  case.  If  .gelatinous  silica  clogs  the  filter,  a 
few  drops  of  hydrofluoric  acid  added  to  the  filtering  liquid  will 
usually  clear  it. 

7.  Treatment  of  Solution. — Having  obtained  a  hydrochloric 
acid  solution  containing  all  the  antimony,  together  with  sufficient 
tartaric  acid,  dilute  to  about  300  cc.  with  hot  water.  If  gela- 
tinous silica  separates,  the  addition  of  i  or  2  cc.  of  strong  hydro- 
fluoric acid  will  usually  cause  it  to  dissolve.  Heat  nearly  to 
boiling  and  pass  in  hydrogen  sulphide  gas  until  the  precipitation 
is  complete.  Filter  off  the  precipitated  sulphides  and  wash 
them  at  least  ten  times  with  hydrogen  sulphide  water  to  remove 
the  hydrochloric  acid.  Now  with  a  jet  of  hot  water  and  using 
as  little  as  possible,  rinse  the  bulk  of  the  precipitate  (through  a 
wide-neck  funnel)  into  an  8-oz.  flask.  Place  the  flask  under  the 
filter  and  dissolve  from  the  latter  any  still  adhering  antimony 
sulphide  with  a  little  warm  ammonium  sulphide.  In  place  of 
these  operations  the  entire  precipitate,  if  its  amount  is  small, 
may  be  extracted  with  ammonium  sulphide  directly  on  the  filter. 


ANTIMONY.  33 

To  the  contents  of  the  flask,  which  need  not  form  a  solution,  add 
3  grams  of  potassium  sulphate  and  8-10  cc.  of  strong  sulphuric 
acid.  This  mixture  now  corresponds  to  that  of  the  original  ore 
described  in  2.  The  addition  of  a  piece  of  filter-paper  is  unneces- 
sary. Follow  the  directions  given  in  2  from  this  point. 

8.  Method    for  Hard  Lead,   etc. — In  the  absence  of  arsenic 
treat  0.5  gram  of  the  alloy,  which  may  be  in  moderately  coarse 
particles,   precisely  as   described   for  ores    (2),   until   the   usual 
melt  is  obtained.     When  cold,  add  50  cc.  of  hot  water  and  10  cc. 
of   strong  hydrochloric   acid.     Heat   until   solution   is   complete 
and  then  boil  off  any  sulphur  dioxide  possibly  present.     Add 
10  cc.  more  of  strong  hydrochloric  acid,  cool  completely  under 
the  tap,  dilute  to  about  140  cc.  with  cold  water  and  titrate  with 
permanganate  as  in  4.      Tin,  lead  and  small  amounts  of  copper 
and  iron  do  not  interfere.     If  arsenic  is  present  it  may  be  removed 
by  volatilization,  as  follows:  Take  up  the  melt  in  25  cc.  of  water 
and  20  cc.  of  strong  hydrochloric  acid.     Boil  the  mixture  until 
only    15  cc.  remain.     Now   add    15  cc.   of   strong   hydrochloric 
acid,  and  cool,  dilute  and  titrate  as  before.     A  concentration  to 
20  cc.  may  fail  to  remove  all  the  arsenic  if  much  is  present,  and  a 
concentration    to    10  cc.  will    occasion    an    appreciable    loss    of 
antimony.     The   procedure   is   therefore   not   perfectly   satisfac- 
tory.    The  safest  way,  when  arsenic  is  liable  to  be  present,  is 
to  treat  the  melt  as  described  for  ores  (3).     An  alloy  containing 
a  large  amount  of  copper  should  be  finely  divided  and  treated 
like  an  ore  (2),  without  modification  of  the  method. 

9.  Another  Method  for  Hard  Lead,  etc. — Treat  0.5  gram  of  the 
very  finely  divided  alloy  in  an  8-oz.  flask  with  a  mixture  of  5  cc. 
strong  nitric  acid,   10  cc.  of  water,  and  2-3  grams  of  tartaric 
acid.      Heat  gently  until  solution  is  complete  and  then  boil  off 
most  of  the  nitric  acid.     Add  sufficient  water  (and  more  tartaric 
acid  if  the  solution  becomes  turbid)  and  pour  the  mixture  slowly 


34  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

into  a  solution  containing  20-25  grams  of  sodium  monosulphide 
and  10  grams  of  sodium  hydroxide  in  300  cc.  of  water.  Warm 
the  mixture,  allow  the  lead  sulphide,  etc.,  to  settle,  and  filter, 
washing  with  water  containing  sodium  sulphide.  Make  the 
nitrate  slightly  acid  with  dilute  sulphuric  acid,  allow  the  pre- 
cipitated antimony  sulphide  to  settle,  and  then  filter  and  wash 
with  dilute  hydrogen  sulphide  water.  Treat  the  antimony 
sulphide  from  this  point  as  described  in  4,  or,  if  arsenic  is  liable 
to  be  present,  proceed  as  follows:  Rinse  the  precipitate  from  the 
filter  as  completely  as  possible  with  a  jet  of  hot  water  into  a 
400-cc.  beaker.  Place  the  beaker  and  contents  under  the  funnel 
and  dissolve  the  precipitate  still  adhering  to  the  filter  with  a 
little  warm  ammonium  sulphide  solution.  Make  the  mixture 
in  the  beaker  just  acid  with  hydrochloric  acid  and  then  add  to 
it  just  double  its  volume  of  strong  hydrochloric  acid.  Warm 
the  mixture  slightly  and  stir  until  all  the  antimony  sulphide 
has  dissolved  and  then  pass  in  hydrogen  sulphide  to  again  pre- 
cipitate any  arsenic  sulphide  that  may  have  also  dissolved. 
Finally,  filter  through  a  double  filter  as  described  in  3,  and  con- 
tinue as  described  in  3  and  4. 

10.  RowelPs  Method  for  Antimony  in  Ores  and  Alloys.* — 
The  following  method  is  based  on  the  reaction 

KBrO3  +3SbCl3  +6HC1  =  3SbCl5  +KBr  +  3H2O. 

A  method  based  on  this  reaction  was  first  suggested  by 
Gyory  and  modified  by  Nissensen  and  Siedler  for  testing  hard 
leads.  The  present  method  is  a  modification  of  the  latter. 

Standard  Arsenious  Chloride  Solution, — 0.8236  gram  of  pure 
powdered  arsenious  oxide,  dried  carefully  at  100°  C.,  is  weighed 

*  H.  W.  Rowell,  Jour.  Soc.  Chsm  Ind.,  XXV,  1181. 


ANTIMONY,  25 

into  a  500  cc.  graduated  flask.  About  5  cc.  of  10  per  cent, 
sodium  hydroxide  solution  are  added,  and  the  flask  shaken  and 
gently  warmed  until  the  arsenic  is  completely  dissolved;  5  cc. 
of  strong  hydrochloric  acid  are  added  and  the  solution  made  up 
to  the  mark  with  water.  Fifty  cubic  centimeters  of  this  solution, 
equivalent  to  o.io  gram  of  antimony,  are  measured  off  with  a 
pipette,  the  delivery  of  which  has  been  checked  against  the 
500  cc.  flask.  A  solution  made  in  this  way  and  kept  in  a  well- 
stoppered  bottle  remains  unchanged  for  a  fortnight  without 
oxidation. 

The  Indicator.  —  o.  i  gram  of  pure  methyl  orange  is  dissolved 
in  100  cc.  of  hot  water.  Drops  of  this  indicator  should  be  taken 
out  with  a  tube  to  avoid  the  stain  left  about  the  neck  of  the 
bottle,  as  this  or  an  old  solution  is  liable  to  leave  a  stain  and 
spoil  the  sharp  finish.  Methyl  blue  and  other  methyl  colors 
stable  in  hydrochloric  acid  generally  stain  the  solution,  while 
indigo  turns  green  toward  the  finish,  and  the  end  is  not  so  easily 
distinguished  as  with  methyl  orange.  More  of  a  solution  of 
indigo  is  also  required  to  produce  a  sufficient  color,  which  makes 
the  test  a  trifle  higher. 

The  Standard  Potassium  Bromate  Solution  is  approximately 
N/20,  and  is  made  by  dissolving  1.41  grams  of  the  "  pure  " 
salt  in  i  liter  of  water.  The  theoretical  quantity  is  i .  3926  grams, 
per  liter,  but  the  "  pure  "  salt  always  contains  bromide  which, 
however,  makes  no  difference  to  the  test.  To  standardize  the 
solution,  20  cc.  of  strong  hydrochloric  acid  are  added  to  50  cc. 
of  the  standard  arsenic  solution,  and  the  mixture  just  brought 
to  the  boil.  Thirty  cubic  centimeters  of  the  bromate  solution 
are  then  added,  and  the  titration  finished  in  exactly  the  same 
way  as  in  the  method  below,  observing  all  the  precautions.  The 
solution  should  be  standardized  every  week,  as  it  loses  value  at 
the  rate  of  about  2.5  cc.  per  liter  per  week. 


36  TECHNICAL    METHODS  OF    ORE   ANALYSIS. 

A  one-fifth  normal  solution  may  be  used  for  titrating  larger 
quantities  of  antimony. 

Bromine  Solution.  —  Thirty-five  cubic  centimeters  of  pure 
bromine,  thoroughly  shaken  up  with  250  cc.  of  strong  hydro- 
chloric acid,  makes  a  saturated  solution,  and  leaves  excess  of 
bromine.  The  required  quantity  is  conveniently  measured  by 
dipping  in  a  pipette  without  any  stem  below  the  bulb  and  so 
allowing  it  to  fill. 

Method  of  Analysis.  —  i  gram  of  the  finely  divided  ore  or  alloy, 
containing  not  more  than  0.15  gram  of  antimony,  is  weighed 
off  into  a  500  cc.  Bohemian  beaker.  These  quantities  may  be 
varied,  provided  that  more  of  the  substance  can  be  conveniently 
dissolved,  and  that  the  amount  of  standard  bromate  solution 
required  is  within  the  compass  of  the  burette  used.  To  the 
sample,  25  cc.  of  concentrated  hydrochloric  acid  and  5  cc.  of 
the  saturated  solution  of  bromine  in  hydrochloric  acid  are  added; 
the  covered  beaker  is  then  placed  on  a  warm  iron  plate,  so  that 
the  temperature  is  not  high  enough  to  drive  off  the  bromine 
before  complete  solution  is  effected,  and  occasionally  shaken 
until  complete  solution  takes  place. 

Antimony  oxides,  and  precipitates  of  mixed  oxides  of  antimony 
and  tin  which  do  not  dissolve  readily  in  this  way,  may  be  fused 
with  eight  times  their  weight  of  caustic  soda  in  a  silver  crucible 
at  a  dull  red  heat,  till  the  mass  turns  yellowish-green.  The 
fused  mass  is  dissolved  in  as  little  water  as  possible  and  trans- 
ferred to  a  500  cc.  beaker  and  the  solution  acidified  with  hydro- 
chloric acid  and  evaporated  down  to  10  cc.,  when  20  cc.  of 
hydrochloric  acid  are  added.  To  reduce  the  antimony,  3  or  4 
grams  of  fresh  sodium  sulphite  crystals  are  added,  the  cover  and 
sides  of  the  beaker  lightly  rinsed  down  with  water,  and  the 
liquid  evaporated,  with  the  cover  on,  to  10  cc.,  or  a  little  less  if 
possible.  Although  there  seems  to  be  little  risk  of  the  antimony 


ANTIMONY.  37 

oxidizing  during  the  evaporation,  the  cover  is  better  kept  on, 
as  it  retards  the  evaporation  very  little  and  often  saves  a  test 
when  it,  or  one  near  it,  spurts  through  evaporating  too  far. 

Sodium  sulphite  is  better  than  sulphurous  acid  for  effecting 
the  reduction,  as  it  raises  the  boiling  point  considerably  toward 
the  finish  and  ensures  complete  volatilization  of  the  arsenic.  If 
more  than  2  or  3  per  cent,  of  arsenic  are  present,  20  cc.  of  strong 
hydrochloric  acid  and  5  cc.  of  saturated  sulphurous  acid  are 
added,  and  the  liquid  boiled  down  again. 

To  the  concentrated  solution,  20  cc.  of  strong  hydrochloric 
acid  and  40  cc.  of  hot  water  are  added,  the  cover  and  sides  of 
the  beaker  are  rinsed,  and  the  whole  is  boiled  for  one  minute 
to  remove  traces  of  sulphurous  acid.  The  standard  solution  of 
potassium  bromate  is  now  run  in  to  within  a  few  cubic  centimeters 
of  the  necessary  amount,  with  constant  and  thorough  stirring, 
and  at  the  rate  of  30  cc.,  at  most,  every  50  seconds.  If  lead 
chloride  begins  to  crystallize,  the  solution  must  be  boiled  again, 
but  otherwise  two  drops  of  methyl  orange  solution  are  added 
and  the  bromate  run  in  drop  by  drop  till  the  color  of  the  indicator 
is  destroyed.  The  solution  should  be  kept  at  a  minimum  tem- 
perature of  60°  C.,  and  should  be  thoroughly  stirred  during  the 
titration  so  that  a  local  excess  of  bromate  never  forms,  otherwise 
some  of  its  value  is  lost  before  attacking  the  antimony.  The 
result  is  calculated  from  the  equation 
(cc.  of  bromate  required  by  i  gram  sample  —  blank)  10  _  ~  «, 

cc.  of  bromate  required  by  50  cc.  of  arsenic  solution 

A  blank  test  should  be  made  occasionally  in  exactly  the  same 
way  as  above,  omitting  the  sample,  and  the  result  (which  should 
not  exceed  0.2  cc.)  subtracted  from  each  test. 

Possible  Sources  of  Error.  —  The  most  probable  sources  of 
error  are  the  incomplete  removal  of  arsenic  or  sulphur  dioxide. 

Oxidation  need  not  be  feared  if  the  cover  is  kept  on.     The 


38  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

liquid  must  not  be  allowed  to  evaporate  to  dryness,  as  antimo- 
nious  chloride  begins  to  volatilize  at  about  195°  C.,  and  boils  at 
220°  C. 

Lead,  zinc,  tin,  silver,  chromium  and  sulphuric  acid  have  no 
effect  upon  the  test,  but  large  quantities  of  calcium  and  ammonium 
salts  tend  to  make  the  result  high. 

Iron  tends  to  make  the  results  high,  but  not  in  as  great  a  ratio 
as  copper.  Iron  is  very  slightly  reduced  by  sulphurous  acid  in 
a  strong  hydrochloric  acid  solution,  and  if,  before  adding  the 
sodium  sulphite  to  a  test,  it  is  boiled  down  to  as  small  volume  as 
possible  and  made  up  again  with  cold,  strong  hydrochloric  acid, 
the  effect  of  iron  is  almost  destroyed.  With  this  precaution,  i 
per  cent,  of  iron  raises  the  test  about  0.02  per  cent.,  while  5  per 
cent,  has  very  little  more  effect. 

The  Effect  of  Copper.  —  Copper  is  partially  reduced  by  sul- 
phurous acid  in  a  strong  hydrochloric  acid  solution,  and,  under 
the  conditions  of  the  method  given,  raises  the  test  in  a  fairly 

constant  ratio  as  shown  by  the  following  figures: 

Gram  Sb. 

o.oo i  gram  of  copper  as  cupric  chloride  in  a  blank  test  =  o.oooi 

0.005   "      "      "     "      "      =  °-00°5 
o.oio   "      "      "     "       "      ==  0.0012 

The  quickest  and  most  satisfactory  way  of  obviating  the  effect 
of  copper  is  to  dissolve  the  substance  in  15  cc.  of  nitric  acid  i  :  2, 
evaporate  just  to  dryness,  and  boil  for  a  few  minutes  with  50  cc. 
of  i  per  cent,  nitric  acid;  allow  to  settle  and  pour  off  the  liquid 
through  a  fine  filter.  Add  30  cc.  of  5  per  cent,  solution  of  ammo- 
nium nitrate,  boil  again,  and  transfer  all  the  precipitate  to  the 
filter,  wash  two  or  three  times  with  a  hot  5  per  cent,  solution  of 
ammonium  nitrate,  and  dry  the  filter  and  precipitate.  Separate 
the  latter  from  the  filter  and  fuse  it  and  the  filter  ash  together  as 
directed  above. 


ANTIMONY.  39 

Perhaps  as  exact  a  way  when  the  copper  amounts  to  about  i 
per  cent,  is  to  subtract  0.012  per  cent,  of  antimony  for  every  o.  i 
per  cent,  of  copper,  the  copper  being  estimated  by  a  separate 
colorimetric  test. 

By  the  above  method  an  estimation  of  antimony  in  antimonial 
lead  can  be  carried  out  in  one  hour  from  the  time  of  weighing. 


CHAPTER   VI. 

ARSENIC. 

FOR  the  technical  determination  of  arsenic  in  ores  and  metal- 
lurgical products  I  have  found  the  following  method  to  be  perhaps 
the  most  generally  applicable  and  reliable  (also  see  n): 

1.  Method  for  Ores,  etc.* — Treat  0.5  gram  of  the  ore  pre- 
cisely as  described   for  the  determination  of  antimony  (v,  2)  up 
to   the  point,  indicated   in  the  text  (v,   3),   where   the   arsenic 
is  obtained  on  the  filter  as  sulphide,  the  antimony  being  in  the 
filtrate.     Now  proceed  as  follows: 

2.  Rinse  out  any  sulphide  adhering  in  the  flask  or  on  the 
delivery-tube   as    completely   as   possible,   pouring   through   the 
filter,  and  then  wash  the  filter  and  contents  well  with  hydrogen 
sulphide  water.     Absolutely  complete  removal  of  the  hydrochloric 
acid  is  unnecessary.     Dissolve  the  arsenic  sulphide   (this  may 
usually  be  done  directly  on  the  filter),  and  also  any  particles  of 
sulphide  on  the  delivery-tube,  with  warm  ammonium  sulphide 
solution  and  wash  with  the  same  solution  diluted,  receiving  the 
filtrate  in  the  original  flask.     To  the  filtrate  add .  i   gram  of 
potassium  sulphate,  3  grams  of  ammonium  sulphate,  and  8  cc. 
of  strong  sulphuric  acid.     Boil  the  mixture  to  a  small  bulk  and 
then  manipulate  the  flask  over  a  free  flame  until  all  the  sulphur 
is  expelled  and  a  clean  melt  of  the  mixed  sulphates  is  obtained. 
Cool  with  the  flask  inclined  as  a  precaution  against  cracking. 

*  A.  H.  Low,  Jour.  Am.  Chem.  Soc.,  XXVIII,  1715.     Modified. 

40 


ARSENIC.  41 

Any  small  amount  of  hydrochloric  acid  present  is  expelled  during 
the  heating  before  the  arsenic  sulphide  is  decomposed,  and 
therefore  causes  no  loss  of  arsenic  by  volatilization  as  chloride. 
Take  up  the  cool  residue  by  warming  with  50  cc.  of  water  and 
then  boil  a  short  time  to  expel  any  possible  sulphur  dioxide. 
Now  cool  to  room  temperature,  add  a  little  starch  solution  (xni, 
2;  this  is  an  acid  solution),  then,  with  a  little  phenolphthalein 
as  indicator,  make  slightly  alkaline  with  a  solution  of  sodium 
hydroxide,  and  again  re-acidify  slightly  with  hydrochloric  acid. 
Cool  once  more  if  necessary.  Finally,  add  3  to  4  grams  of  sodium 
acid  carbonate  and  titrate  with  standard  iodine  solution.  Pay 
no  attention  to  a  brownish  discoloration  toward  the  end,  but 
proceed  slowly  until  a  single  drop  of  the  iodine  solution  produces 
a  strong  permanent  blue  color.  If  neutral  starch  liquor  is  used 
it  need  not  be  added  until  just  before  ti -ration. 

3.  The  iodine  solution  may  be  prepared  by  dissolving  about 
ii  grams  of  iodine  in  a  little  water,  with  the  addition  of  about 
20  grams  of  potassium  iodide,  and  diluting  to  i  liter.    Standardize 
with  pure  powdered  arsenious  oxide.     Dissolve  about  0.150  gram 
by  warming  gently  in  an  8-oz.  flask  with  a  little  sodium  hydroxide 
solution.     Dilute   somewhat,   cool,   add  starch,   neutralize,   etc., 
similarly  to  the  above  and  finally  titrate  with  the  iodine  solution. 
One  cubic  centimeter  of  the  latter  will  equal  about  0.003  gram 
of  arsenic.     Multiply  the  weight  of  As2Os  taken  by  0.7575  to 
obtain  the  equivalent  weight  of  As. 

A  small  amount  of  copper  is  without  influence  in  the  titration 
provided  it  remains  in  solution.  If  a  precipitate  of  copper 
arsenite  is  formed,  add  a  little  ammonium  chloride  to  dissolve  it. 

4.  Method  for  Lead,  Copper,    Alloys,  etc. — It  will  frequently 
suffice  to  take  0.5  gram  of  the  finely  divided  material  and  treat 
it  as  just  described  for  ores.     Or,  the  method  described  in  v,  9, 
may  be  followed  until  the  arsenious  sulphide,  free  from  antimony, 


42  TECHNICAL   METHODS    OF   ORE  ANALYSIS. 

is  obtained  on  the  double  filter.     From  this  point  follow  the 

directions  given  in  2. 

5.  Pearce's  Method,  Modified.* — Thoroughly  mix  0.5  gram 
of  the  finely  ground  ore  in  a  platinum  dish  or  large  porcelain 
crucible,  with  5  grams  of  a  mixture  of  equal  parts  of  dry  sodium 
carbonate  and  potassium  nitrate.  It  is  a  good  plan  to  reserve 
a  portion  of  the  mixed  salts  for  use  as  a  cover.  Heat  the  mass 
gradually  over  a  Bunsen  burner  to  complete  fusion.  It  is  best 
to  use  a  very  low  flame  at  first  and  take  plenty  of  time  so  that 
the  mixed  salts  will  melt  and  soak  through  the  mass  before  much 
decomposition  occurs;  in  this  way  loss  of  arsenic  is  prevented 
with  some  ores  that  tend  to  lose  arsenic  by  volatilization.  Finally, 
heat  to  the  full  power  of  the  Bunsen  burner  until  thorough  decom- 
position is  effected.  Prolonged  heating  over  a  blast- lamp  is 
sometimes  necessary,  especially  with  oxidized  ores  containing 
lead. 

6.  The  melted  mass  should  finally  present  a  smooth  and 
homogeneous  appearance  if  the  dish  or  crucible  is  taken  up  in 
the  tongs  and  given  a  circular  movement.  Cool,  extract  the  sol- 
uble portion  by  heating  with  water  until  thoroughly  disintegrated, 
and  then  filter  and  wash  the  residue  with  cold  water.  Receive 
the  filtrate  in  a  6-oz.  flask.  Drop  a  bit  of  litmus  paper  into  the 
flask  and  then  add  nitric  acid  carefully  until  the  solution  is  plainly 
acid,  simply  avoiding  a  large  excess,  but  if  a  precipitate  has 
formed  always  add  enough  acid  to  dissolve  it.  Now  add  a 
sufficient  quantity,  as  explained  below,  of  a  solution  of  silver 
nitrate,  which  will  usually  cause  a  white  precipitate  of  silver 
chloride,  and  then  cautiously  add  ammonia  until,  if  arsenic  be 
present,  a  reddish  precipitate  of  silver  arsenate  appears.  If  too 

*  This  method  was  originally  developed  by  Dr.  Pearce  and  the  author  in  the 
laboratory  of  the  Boston  and  Colorado  Smelting  Works,  at  Argo,  Colorado. 


ARSENIC.  43 

much  ammonia  be  added,  the  precipitate  first  formed  will  redis- 
solve  and  may  not  be  observed  at  all.  In  this  case  the  bit  of 
litmus  paper  in  the  liquid  will  show  an  alkaline  reaction.  Now 
cautiously  add  nitric  acid  (best  dilute)  until  the  red  precipitate 
just  redissolves  or  the  litmus  paper  shows  a  slight  acid  reaction. 
To  the  faintly  acid  liquid  add  a  few  cubic  centimeters  of  a  strong 
solution  of  sodium  acetate  or  i  or  2  grams  of  the  crystals.  This 
will  effect  a  replacement  of  the  free  nitric  acid  with  acetic  acid 
and  all  the  arsenic  will  be  at  once  precipitated  as  silver  arsenate, 
Ag3As04. 

In  order  to  avoid  an  unnecessarily  large  excess  of  silver  nitrate, 
it  is  best  to  make  up  a  solution  containing,  say,  17  grams  in 
500  cc.  and  use  a  definite  amount,  i  cc.  of  a  solution  of  this 
strength  will  precipitate  0.005  gram  of  arsenic,  or  i  per  cent, 
if  0.5  gram  of  ore  is  taken  for  assay.  Thus  10  cc.  will  be  an 
excess  in  most  cases.* 

Heat  the  precipitated  mixture  to  boiling  and  then  cool  to 
room  temperature,  allowing  the  precipitate  to  settle  somewhat, 
and  filter.  If  the  first  portions  run  through  turbid,  return 
them  to  the  filter  once  more.  Test  the  filtrate  with  a  little  more 
silver  nitrate  and  sodium  acetate.  Wash  the  precipitate  with 
cold  water  until  a  portion  of  the  washings  shows  only  a  faint 
cloud  when  tested  for  silver  with  a  soluble  chloride. 

Now  place  the  original  flask  under  the  funnel  and  dissolve 
the  arsenate  on  the  filter  with  cold  dilute  (1:1)  nitric  acid;  5  or 
10  cc.  will  usually  suffice.  Wash  the  filter  thoroughly  with  cold 
water.  A  white  residue  of  silver  chloride  usually  remains  undis- 
solved.  Dilute  the  filtrate,  if  necessary,  to  about  100  cc.,  add 
about  5  cc.  of  a  strong  solution  of  ammonio-ferric  alum,  and  titrate 
to  a  permanent  red  tinge  with  a  solution  of  ammonium  thiocy- 
anate  (Volhard),  shaking  well,  especially  at  the  end,  to  break  up 
the  clots  of  precipitate  and  free  any  solution  held  mechanically. 

*  It  is  best  to  use  at  least  10  cc.  in  every  case,  as  small  amounts  of  arsenic  may 
entirely  fail  to  precipitate  unless  a  considerable  excess  of  silver  nitrate  be  added. 


44  TECHNICAL   METHODS  OF   ORE  ANALYSIS. 

Multiply  the  number  of  cubic  centimeters  required,  by  the 
arsenic  value  of  i  cc.  to  obtain  the  amount  of  arsenic  in 
the  ore. 

7.  If  the  thiocyanate  solution  contains  7.612  grams  of 
NH4SCN  per  liter,  i  cc.  will  equal  0.0025  gram>  or  °-5  percent., 
of  arsenic.  It  should  be  standardized  carefully,  either  against 
pure  silver  or  silver  nitrate,  which  contains  63.51  per  cent,  of 
silver.  Weigh  accurately  about  0.5  gram  of  pure  silver,  dis- 
solve in  a  little  nitric  acid,  and  dilute  to  about  100  cc.,  or,  instead, 
weigh  about  0.8  gram  of  silver  nitrate  and  dissolve  in  100  cc.  of 
water  acidified  slightly  with  nitric  acid.  In  either  case  add  a 
few  cubic  centimeters  of  a  strong  solution  of  ammonio-ferric  alum 
(acidified  with  a  little  nitric  acid)  as  an  indicator,  and  titrate  to 
a  faint-red  tinge  with  the  thiocyanate  solution  as  described  above. 
From  the  number  of  cubic  centimeters  required  and  the  weight 
of  silver  taken,  determine  the  value  of  i  cc.  in  silver.  The  formula 
of  the  red  precipitate,  Ag3AsO4,  shows  that  107.93  parts  of  silver 
represent  25  parts  of  arsenic,  and,  accordingly,  the  arsenic  value 
of  i  cc.  of  the  thiocyanate  solution  is  easily  deduced  from  the 
silver  value  by  proportion. 

8.  When  testing  heavy  sulphide  ores  there  is  some  danger 
of  a  loss  of  arsenic  by  volatilization  during  the  deflagration. 
To  avoid  this  proceed  as  follows:  Cover  the  dish,  containing  the 
weighed  ore,  with  a  watch-glass.  Add  a  little  nitric  acid  and 
then  heat  gently,  with  the  cover  on,  to  complete  dryness.  The 
dish  may  be  placed  above  a  small  free  flame  and  the  heat  increased 
at  the  end.  Allow  to  cool,  loosen  any  spatterings  on  the  cover 
with  a  moistened  rubber-tipped  glass  rod,  and  rinse  them  into 
the  dish  with  as  little  water  as  possible.  It  is  usually  unnecessary 
to  evaporate  off  this  water  if  the  amount  is  small.  Add  the  5 
grams  of  nitrate  mixture,  heat  cautiously  to  dryness,  and  then 
fuse  and  proceed  as  usual. 


ARSENIC. 


45 


9.  Sodium  Carbonate  and  Zinc  Oxide  Method  for  Ores,  etc.* 

—Thoroughly  mix  i  part  of  dry  sodium  carbonate  and  4  parts 
of  zinc  oxide.  Weigh  0.5  gram  of  the  ore  into  a  platinum  dish 
and  intimately  mix'  it  with  3  grams  of  the  above  mixture,  then 
cover  with  2  grams  more.  Partially  cover  the  dish  with  a 
thin  piece  of  asbestos  board,  so  as  to  keep  in  the  heat,  and 
heat  over  a  Bunsen  burner  to  bright  redness  for  about 
twenty  minutes.  An  uncovered  porcelain  dish  may  be  used, 
similarly  heated  in  a  muffle.  Allow  to  cool  and  transfer  the 
mass  to  a  suitabfe*  beaker,  rinsing  out  the  dish  with  hot  water 
and  making  up  the  bulk  in  the  beaker  to  about  50  cc.  Heat  the 
mixture  to  boiling,  stirring  well,  and  filter,  washing  thoroughly 
with  hot  water.  Receive  the  filtrate-  in  an  8-oz.  flask.  Drop  a 
small  bit  of  litmus  paper  into  the  solution  as  an  indicator  and 
then  make  slightly  acid  with  acetic  acid.  Now  add  an  excess 
of  silver  nitrate  solution,  as  described  in  6,  and  agitate  the 
mixture  occasionally  for  a  few  minutes  without  heating.  Filter 
the  silver  arsenate,  refiltering  if  any  runs  through,  and  finish 
the  determination  as  described  in  6. 

Note. — For  an  arsenic  determination,  wh^re  antimony  is  not 
also  required,  this  method  is  shorter  and  simpler  than  either 
of  those  previously  described,  but  I  have  found  it  inapplicable 
to  oxidized  ores  containing  much  lead,  as  some  of  the  arsenic 
always  combines  with  the  lead  and  fails  to  be  extracted.  A 
determination  can  easily  be  made  in  about  fifty  minutes.  The 
following  test  indicates  that  antimony  does  not  interfere: 

An  oxidized  ore  treated  by  my  own  methods  gave 

Arsenic 9-365  per  cent. 

Antimony 0.47 

*  W.  C.  Ebaugh  and  C.  B.  Sprague,  Jour.  Am.  Chem.  Soc.,  XXIX,  1475. 


46  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

In  trying  the  above  method  with  this  ore,  0.5  gram  was 
weighed  into  a  platinum  dish  and  o.i  gram  of  80203  added. 
This  was  equivalent  to  increasing  the  antimony  contents  of  the 
ore  to  about  17  per  cent.  Two  grams  of  the  zinc  oxide  mixture 
were  intimately  mixed  with  the  above  and  about  a  gram  more  was 
used  as  a  cover.  The  dish  and  contents  were  kept  at  a  bright 
red  heat  over  a  Bunsen  burner  for  15  minutes  and  the  assay  then 
finished  as  described.  Found,  arsenic,  9.365  per  cent,  exactly 
checking  my  result  by  the  other  method. 

10.  Method  of  L.  L.  Krieckhaus.* — Decompose  0.5  gram  of 
the  ore  with  the  zinc  oxide  mixture  precisely  as  described  in  9. 
Receive  the  filtrate  in  an  8-oz.  flask  and  boil  it  down  to  50  cc. 
After  cooling,  add  50  cc.  of  strong  hydrochloric  acid  and  again 
cool.  Now  add  10  cc.  of  a  20  per  cent  potassium  iodide  solution 
(the  solid  salt  would  fail  to  properly  dissolve  in  the  strong  acid) 
and  allow  a  minute  for  the  reaction  to  become  complete,  as 
follows: 

H3AsO4  +  2HI  =  H3AsO3  +  H2O  + 12. 

This  reaction  can  be  made  to  go  completely  in  either  direction 
according  to  the  conditions,  f  In  the  strongly  acid  solution 
prescribed  it  proceeds  as  written.  Now  add  about  100  cc.  of 
cold  water  and  titrate  to  complete  dect>lorization  with  a  standard 
solution  of  sodium  thiosulphate.  No  indicator  is  required,  as  the 
end-point  is  easily  observed.  The  thiosulphate  solution  used 
in  the  iodide  method  for  copper  (xin,  i)  may  be  employed. 
The  copper  value  multiplied  by  0.59  will  give  the  arsenic 
value. 

When  the  solution  of  the  sintered  mass,  after  the  decom- 
position, is  colored  green  or  pink  by  manganese,  add  5  cc.  of 

*  Eng.  and  Min.  Jour.,  Vol.  90,  357. 

t  E.  W.  \\ashburn,  Jour.  Am.  Chem.  Soc.,  XXX,  31. 


ARSENIC.  47 

alcohol  or  hydrogen  peroxide  and  boil  to  precipitate  the  manga- 
nese before  nitration.  Chromium,  if  present,  interferes  as  in 
the  Pearce  method.  Phosphorus  does  not. 

I  have  found  this  an  excellent  method.  The  treatment  of  the 
nitrate  is  simpler  than  the  procedure  of  Sprague  and  Ebaugh 
and  the  result  quite  as  accurate.  There  is  the  same  objection 
to  both  methods,  however,  and  that  is  the  difficulty  of  decom- 
posing oxidized  lead  ores  so  as  to  form  a  soluble  alkali  arsenate. 
Acting  on  Krieckhaus'  idea,  I  have  devised  the  following  method, 
which  appears  to  overcome  this  objection  and  be  suitable  in  all 
cases,  although  I  have  not  had  the  opportunity,  as  yet,  of  making 
many  comparative  tests. 

ii.  Author's  Zinc  Oxide  Method. —  Prepare  a  mixture  of 
i  part  sodium  carbonate,  i  part  potassium  nitrate,  and  2  parts 
zinc  oxide.  To  0.5  gram  of  the  ore  in  a  platinum  dish  add 
5  grams  of  this  mixture  and  grind  intimately  together  with  an 
agate  pestle.  Heat  the  dish  and  contents  gradually  to  dull 
redness,  then  to  bright  redness  for  perhaps  ten  minutes.  If 
a  Bunsen  burner  is  used,  nearly  cover  the  dish  with  a  piece  of  thin 
asbestos  board  to  prevent  radiation.  A  porcelain  crucible  and 
muffle  heating  may  be  employed  if  desired.  Cool,  disintegrate 
the  sintered  mass  with  hot  water  and  filter,  washing  the  residue 
on  the  filter  six  or  seven  times  with  hot  water.  Receive  the 
filtrate  in  an  8-oz.  flask.  Add  to  the  filtrate  6  cc.  of  strong  sul- 
phuric acid  (this  should  be  an  ample  excess)  and  boil  to  strong 
sulphuric  acid  fumes.  The  final  heating  is  best  done  over  a  free 
flame.  Allow  to  cool,  add  50  cc.  of  water,  heat,  if  necessary, 
to  effect  solution,  cool  again,  and  add  50  cc.  of  strong  hydro- 
chloric acid.  Once  more  cool  the  slightly  warm  solution,  add 
4  cc.  of  a  50  per  cent,  solution  of  potassium  iodide  (this  is  the 
usual  solution  for  the  iodide  method  for  copper),  mix  and  allow 
to  stand  about  a  minute.  Now  add  100  cc.  of  cold  water  and 


48  TECHNICAL   METHODS    OF    ORE  ANALYSIS. 

titrate  with  sodium  thiosulphate  solution  as  in  10.  It  is  best 
to  run  a  blank  and  deduct  for  the  drop  or  so  of  thiosulphate 
required.  Chromium  and  phosphorus  do  not  interfere,  nor  does 
any  small  amount  of  manganese  that  may  pass  in  solution  through 
the  filter. 


CHAPTER  Vii. 
BARIUM. 

i.  Method  for  Ores. — Decompose  0.5  gram  of  the  ore  in  a 
4-oz.  Erlenmeyer  flask,  or  a  covered  beaker,  by  one  of  the  methods 
described  for  INSOLUBLE  RESIDUE  (xxiv),  according  to  its 
nature.  When  solution  is  as  complete  as  possible  add  a  few 
drops  of  strong  sulphuric  acid  to  make  sure  that  all  the  barium 
will  be  rendered  insoluble.  Dilute  the  mixture  with  about  50  cc. 
of  water,  heat  to  boiling,  and  filter,  washing  with  hot  water.  If 
the  ore  contains  lead  add  about  5  grams  of  ammonium  chloride 
before  boiling  and  filtering,  in  order  to  retain  it  all  in  solution. 
Place  the  filter  and  insoluble  residue  containing  the  barium 
in  a  platinum  dish  or  crucible  and  ignite  to  burn  off  the  filter- 
paper.  Mix  the  cold  residue  with  3-5  grams  of  mixed  sodium 
and  potassium  carbonates  and  fuse  for  a  short  time  to  convert 
the  barium  to  carbonate  After  cooling,  heat  the  melt  with  water 
until  disintegration  is  complete.  If  a  platinum  dish  has  been 
used  it  will  probably  hold  sufficient  water  for  the  purpose;  a 
platinum  crucible  may  be  placed  in  water  in  a  beaker.  Filter, 
washing  with  dilute  ammonia  water  until  sulphates  are  all 
rernoved.  If  desired,  the  filtrate  may  be  tested  from  time  to 
time  by  collecting  a  portion  in  a  test-tube,  slightly  acidifying 
with  hydrochloric  acid,  then  adding  a  little  barium  chloride 
solution  and  warming.  When  no  white  precipitate  of  barium 
sulphate  forms  the  washing  is  sufficiently  complete. 

49 


50  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Rinse  the  more  or  less  impure  barium  carbonate  on  the  filter 
as  completely  as  possible  into  a  small  beaker.  Some  barium 
carbonate  will  still  remain  on  the  filter,  and  there  may  also  be  a 
little  adhering  in  the  dish  or  crucible  used  for  the  fusion.  Dis- 
solve the  latter  in  5  cc.  of  strong  hydrochloric  acid  and  then 
transfer  this  to  the  beaker  containing  the  bulk  of  the  carbonate, 
covering  at  once  with  a  watch-glass  to  avoid  loss  by  spattering. 
Warm  the  solution,  wash  off  the  cover  and  remove  it  and  then 
pour  the  liquid  through  the  filter  last  used,  so  as  to  dissolve 
whatever  barium  carbonate  was  left  there.  Wash  beaker  and 
filter  with  hot  water  and  receive  the  filtrate  in  a  large  beaker. 
Dilute  to  about  300  cc.,  heat  nearly  to  boiling,  and  add  about 
3  cc.  of  strong  sulphuric  acid  diluted  with  sufficient  water  to 
prevent  violent  action.  Cover  the  beaker  and  allow  to  stand, 
hot,  for  several  hours,  best  over  night,  to  insure  the  complete 
precipitation  of  the  barium  sulphate.  Finally  filter  and  wash 
well  with  hot  water.  The  precipitate  is  very  fine  and  will  run 
through  a  loosely  woven  filter.  The  best  Swedish  or  German 
filters  usually  give  no  trouble.  It  is  safest  to  decant  carefully 
through  the  filter  without  disturbing  the  precipitate  in  the  bot- 
tom until  most  of  the  clear  liquid  is  gone,  then  remove  the  beaker 
containing  the  filtrate  and  replace  it  with  another,  so  that  if  the 
barium  sulphate  runs  through  there  will  be  less  liquid  to  re- 
filter.  The  combined  filtrate  and  washings  should  be  allowed 
to  stand,  hot,  for  a  while  longer,  to  be  certain  that  the  precipi- 
tation is  complete.  The  moist  precipitate  and  filter  may  be 
ignited  together  over  a  Bunsen  burner  in  a  weighed  platinum  or 
porcelain  crucible.  The  strong  heat  of  a  blast-lamp  should 
not  be  employed.  The  carbonaceous  matter  of  the  filter  may 
reduce  some  of  the  barium  sulphate  to  sulphide,  but  ignition 
with  free  access  of  air  will  easily  effect  reoxidation.  The  ignited 
barium  sulphate  should  be  perfectly  white.  The  weight  of  the 


BARIUM.  51 

BaSC>4  multiplied  by  0.657  w^  giye  tne  corresponding  weight 
of  BaO  if  the  latter  is  required. 

In  rapid  technical  work  it  is  usually  sufficient  to  ignite  the 
barium  sulphate  in  a  small  clay  "annealing-cup,"  and,  when 
cold,  shake  and  brush  it  from  the  cup  to  the  scale-pan  for  weighing. 

In  smelter  practice  the  barium  is  usually  required  to  be  re- 
ported as  sulphate,  and  all  the  barium  in  the  ore  is  considered 
as  existing  as  sulphate. 

2.  Short  Method.  —  The  following  method,  though  not  so 
reliable,  will  frequently  serve  for  technical  purposes: 

Having  obtained  the  insoluble  residue,  including  the  barium 
sulphate  as  above,  ignite  it  in  a  small  platinum  dish  to  burn 
off  the  filter-paper,  and  then,  after  cooling,  add  a  few  cubic 
centimeters  each  of  strong  hydrochloric  and  hydrofluoric  acids,  in 
the  order  named,  and  evaporate  on  the  water-bath  nearly  or  quite 
to  dryness.  It  is  best  to  repeat  the  operation  to  insure  the  com- 
plete expulsion  of  the  silicic  acid.  Finally,  take  up  in  hydro- 
chloric acid,  dilute  with  hot  water,  and  filter.  Wash  the  residue 
well  with  hot  water  and  then  ignite  and  weigh  as  BaSQ4  as 
described  above. 


CHAPTER  VIII. 

BISMUTH. 

i.  Method  for  Ores,  etc. — Treat  0.5  gram  of  the  ore  in  an 
8-oz.  flask  with  6-10  cc.  of  strong  nitric  acid  and  boil  nearly  to 
dryness.  Add  5  cc.  of  strong  hydrochloric  acid,  or  more  if  neces- 
sary, and  heat  gently  until  solution  is  as  complete  as  possible, 
and  then  add  10  cc.  of  strong  sulphuric  acid  and  expel  the  more 
volatile  acids  by  boiling  over  a  free  flame  until  fuming  strongly. 
Cool  and  add  25  cc.  of  water  and  boil  gently  a  few  minutes  to 
insure  solution  of  all  the  bismuth  sulphate.  Cool  again,  filter, 
and  wash  with  dilute  sulphuric  acid  (i-io).  Do  not  allow  to 
stand  too  long  before  filtering  or  some  basic  bismuth  sulphate 
may  separate.  Dilute  the  filtrate  somewhat  and  pass  in  a  current 
of  hydrogen  sulphide  to  saturation.  Bismuth,  copper,  arsenic, 
antimony,  etc.,  are  precipitated  as  sulphides.  Filter,  washing 
with  weak  hydrogen  sulphide  water.  Rinse  the  precipitate  as 
completely  as  possible  into  a  beaker,  add  3-4  grams  of  pure 
potassium  cyanide,  and  warm  gently  for  some  time.  Bismuth 
sulphide  will  remain  undissolved,  also  cadmium  sulphide  if 
present  and  any  lead  that  may  not  have  been  removed  as  sulphate. 
Filter  through  the  same  filter  as  before,  in  order  to  act  upon 
the  traces  of  sulphides  that  could  not  be  washed  into  the  beaker, 
and  wash  with  hot  water.  Spread  out  the  filter  on  a  watch- 
glass  and  rinse  off  the  sulphides  into  a  beaker.  To  any  adher- 
ing residue  on  the  filter  add  a  little  dilute  (1:2)  nitric  acid  and 
warm  until  dissolved.  Now  rinse  this  in  with  the  main  portion, 
add  a  little  strong  nitric  acid  if  necessary,  warm  the  mixture  until 

the  bismuth  is  all  in  solution  and  the  separated  sulphur  clean. 

52 


BISMUTH.  53 

Dilute  a  little  and  then  filter  and  wash  thoroughly  with  i :  2 
nitric  acid.  Dilute  the  filtrate  contained  in  a  large  beaker  to 
about  300  cc.  and  heat  to  boiling.  Nearly  neutralize  the  hot 
solution  with  dilute  ammonia  and  precipitate  the  bismuth  as 
basic  chloride  precisely  as  described  for  refined  lead  (6).  Only 
one  precipitation  will  be  necessary.  Collect  the  precipitate  on 
a  weighed  filter,  or  a  Gooch  crucible,  dry  at  100°  C.,  and  weigh 
as  BiOCl.  Multiply  the  weight  found  by  0.8017  to  obtain  the 
weight  of  the  bismuth. 

2.  Instead   of   precipitating   the   bismuth   as   basic   chloride, 
it  may,  in  the  absence  of  lead  and  cadmium,  be  precipitated  as 
basic  carbonate  as  follows:    Partially  neutralize  the  filtrate  from 
the  solution  of  the  bismuth  sulphide  in  nitric  acid  with  ammonia, 
but  without  producing  any  permanent  precipitate,  and  then  add  a 
solution  of  ammonium  carbonate  in  very  slight  excess.     Heat 
nearly  U>  boiling  for  some  time,  until  the  bismuth  carbonate  has 
settled  well,  and  then  filter  and  wash  with  hot  water.     Dry  the 
precipitate*  and  transfer  it  to  a  small  weighed  porcelain  crucible, 
removing  it  from  the  paper  as  completely  as  possible     Burn  the 
latter  carefully  and  add  the  ash  to  be  precipitated  in  the  crucible. 
Ignite  the  whole  at  a  low  red  heat,  cool,  and  weigh  as  Bi2O3- 
Multiply  the  weight  found  by  0.8966  to  obtain  the  weight  of  the 
bismuth. 

The  oxidation  of  the  bismuth  sulphide  by  nitric  acid  may 
produce  some  bismuth  sulphate,  which  would  cause  a  slight  con- 
tamination of  the  basic  bismuth  carbonate  with  basic  sulphate, 
and  the  latter  would  fail  to  be  converted  to  oxide  by  ignition. 
The  error  thus  introduced  is  ordinarily  sufficiently  small  to  be 
negligible  in  technical  work.  If,  however,  greater  accuracy 
is  desired,  the  bismuth  may  be  reduced  to  metal  by  the  method 
of  H.  Rose,  as  follows : 

3.  To  the  ignited  oxide  in  the  crucible  add  about  five  times 


54  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

its  weight  of  pure  potassium  cyanide  and  fuse  the  mixture  over 
a  Bunsen  burner  with  the  flame  at  about  half  the  usual  height. 
Under  these  conditions  there  is  no  danger  of  volatilizing  bismuth, 
which  boils  at  about  1600°  C.  The  reduction  is  usually  com- 
plete in  about  20  minutes.  Extract  the  cold  melt  with  warm 
water  so  as  to  dissolve  the  salts  and  leave  the  metallic  bismuth. 
The  latter  may  be  in  one  or  more  globules,  either  loose  or  adher- 
ing to  the  crucible,  and  usually  contaminated  with  particles  of 
the  glaze.  To  prevent  loss  of  these  particles,  filter  the  aqueous 
extract  through  a  filter  that  has  been  dried  at  100°  C.  and  weighed 
with  the  empty  crucible.  After  extracting  and  washing  thor- 
oughly with  water,  wash  with  absolute  alcohol  and  ether  and 
then  place  the  filter  again  in  the  crucible,  dry  at  100°  C.,  cool, 
and  weigh.  The  gain  in  weight  over  the  original  weight  of 
the  filter  and  empty  crucible  represents  the  metallic  bismuth. 

4.  Electrolytic  Method  for  Ores.  —  The  deposition  of  an 
adherent  coating  of  bismuth  on  a  cathode  of  the  size  herein 
described,  and  under  the  conditions  named,  requires  that  not 
much  more  than  0.03  gram  of  bismuth  shall  be  present.  This 
may  be  regulated  either  by  the  amount  of  ore  taken  for  assay 
or  by  taking  only  a  portion  of  the  final  solution  of  bismuth  for 
electrolysis.  The  quantity  of  bismuth  present  in  an  ore  may 
be  roughly  judged  by  the  bulk  of  the  BiS  precipitate. 

Take  0.5  gram  of  ore  and  proceed  precisely  as  described 
above  (i)  until  the  separated  bismuth  sulphide  has  been  dis- 
solved in  dilute  nitric  acid  and  the  solution  filtered,  the  filtrate 
being  received  in  an  8-oz.  flask.  Now  add  6-7  cc.  of  strong  sul- 
phuric acid  and  boil  to  white  fumes  over  a  free  flame.  Cool,  dilute 
with  25  cc.  of  water,  and  boil  gently  until  all  the  bismuth  sulphate 
is  dissolved.  No  appreciable  amount  of  lead  sulphate  should 
be  found.  Cool,  transfer  to  the  proper  beaker,  and  dilute  to 
,100  cc.  with  cold  water.  The  solution  is  now  ready  for  elec- 


BISMUTH.  55 

trolysis.  The  beaker  and  electrodes  may  be  the  same  as  used 
for  copper,  as  follows.  (See  chapter  on  ELECTROLYSIS.) 

Beaker.  Diameter,  about  5  cm.;  height,  about  8-9  cm. 
Have  a  mark  at  the  ico-cc.  point. 

Electrodes.  The  cathode  is  a  platinum  cylinder  5  cm.  long 
and  2.5  cm.  in  diameter.  This  gives  a  total  surface  of  about 
78.5  sq.  cm.  With  a  current  of  0.6  ampere,  ND 100  =  0.76.  The 
weight  of  this  electrode  is  about  12.5  grams. 

The  anode  is  a  stout  platinum  wire  with  a  flat  spiral  base, 
the  straight  portion  of  the  wire  rising  out  of  the  center  of  the 
base  at  right  angles.  Its  weight  is  about  8.5  grams.  In  use 
the  anode  is  placed  within  the  cathode  with  the  base  a  little 
below  the  lower  edge  of  the  cylinder. 

Arrange  the  weighed  electrodes  in  the  beaker  so  that  the 
top  of  the  cylinder  projects  a  little  above  the  surface  of  the  liquid 
and  cover  the  beaker  with  the  two  halves  of  a  split  watch-glass. 
Electrolyze  with  a  current  of  0.6-0.7  ampere;  electrode  tension 
about  2.7-3  v°lts.  In  rj  hours  remove  and  weigh  the  cathode. 
To  do  this,  disconnect  and  lift  it  from  the  beaker,  at  the  same 
time  washing  it  with  a  gentle  stream  of  water,  and  then  immerse 
it  in  a  beaker  of  water.  Lift  it  from  this,  wash  off  the  water 
with  alcohol,  dry  at  100°  C.,  cool,  and  weigh.  Now  dissolve 
off  the  bismuth  with  nitric  acid  and  ignite  and  weigh  once  more, 
and  then  replace  in  beaker  and  electrolyze  for  another  half  hour, 
when  both  electrodes  may  be  removed  and  weighed.  A  slight 
deposit  of  Bi2O5  is  usually  found  on  the  anode.  Calculate  this 
to  Bi  and  add  the  weight  to  that  of  the  cathode  deposit.  It  is 
well  to  again  clean  and  replace  the  electrodes  and  electrolyze  for 
a  while  longer  to  be  sure  of  obtaining  the  last  traces  of  bismuth. 
Finally,  test  the  exhausted  solution  with  hydrogen  sulphide  water. 

5.  In  case  the  bulk  of  the  bismuth  sulphide  indicates  more 
than  6  per  cent,  bismuth  in  the  ore,  proceed  as  follows:  Dilute 


56  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

the  filtered  nitric  acid  solution  of  the  bismuth  sulphide  to  250  cc., 
adding  more  acid  if  a  basic  salt  begins  to  separate,  and  then 
continue  the  analysis  with  a  suitable  aliquot  portion.  If  the 
percentage  of  bismuth  is  approximately  known  the  proper  amount 
of  ore  may  be  taken  at  the  outset. 

6.   Bismuth   in  -Refined  Lead.*  —  Dissolve  25  grams  of  the 
lead,  best  rolled  or  hammered  out  thin  and  cut  into  small  pieces, 
in  a  mixture  of  250  cc.  of  water  and  40  cc.  of  nitric  acid  of  1.42 
sp.  gr.,  using  a  large  covered  beaker.     Warm  gently  until  all 
the  lead  is  dissolved,  then  remove  the  beaker  from  the  heat  and 
to  the  hot  solution  add  dilute  ammonia  (J  strong  ammonia  and 
|  water)  very  cautiously,  finally  drop  by  drop,  until  the  free  acid 
is  neutralized  and  the  liquid  remains  faintly  opalescent.     There 
should  not  be  a  visible  precipitate  but  just  a  faint  cloudiness, 
Now  add  i  cc.  of  dilute  hydrochloric  acid,  1:3.     The  solution 
will  clear  for  an  instant  and  then,  if  any  considerable  amour t 
of  bismuth  is  present,  a  crystalline  precipitate  of  bismuth  oxy- 
chloride  will  form.     Again  place  the  beaker  over  the  heat  so  the 
liquid  will  keep  hot  but  not  boil.     In  an  hour  the  bismuth  oxy- 
chloride,   together  with  a  little  lead,  will  have  settled.     Filter 
off  the  precipitate  and  wash  it  once  or  twice  with  boiling  water. 
In  addition  to  bismuth  and  lead,  the  precipitate  may  contain 
some    antimony,   if   any   appreciable   quantity   of   the    latter   is 
present  in  the  sample.     Dissolve  the  precipitate  on  the  filter  in 
a  small  quantity  of  hot  dilute  hydrochloric  acid  1:3,  wash  the 
filter  with  hot  water  and  dilute  the  filtrate  with  water,  taking 
care  not  to  make  the  liquid  so  dilute  as  to  cause  a  precipitation 
of  the  bismuth"  as  basic  chloride.     Pass  hydrogen  sulphide  into 
the  liquid  to  precipitate  all  the  bismuth,  lead,  and  antimony  as 
sulphides,   filter,  wash  once  with  water  and  twice  with  warm 
ammonium   sulphide   to   dissolve   the   antimony   sulphide,    and 

*  Ledoux  &  Co. 


BISMUTH.  57 

then,  after  washing  once  more  with  water,  dissolve  the  precipi- 
tate of  bismuth  and  lead  sulphides  by  placing  filter  and  contents 
in  a  small  beaker  and  heating  with  dilute  nitric  acid  (1:4).  Boil 
so  as  to  thoroughly  disintegrate  the  filter-paper  and  then  dilute 
somewhat  with  hot  water  and  filter.  Wash  the  filter  well,  first 
with  a  little  warm  dilute  nitric  acid  (1:4)  and  then  with  hoc 
water.  Partially  neutralize  the  nitric  acid  in  the  filtrate  with 
ammonia,  dilute  with  warm  water  to  a  volume  of  about  300  cc., 
and  then  complete  the  neutralization  and  add  i  cc.  of  dilute 
hydrochloric  acid  as  described  above  for  the  original  precipita- 
tion. The  bismuth  will  now  come  down  as  basic  chloride  free 
from  lead.  Filter  on  a  weighed  filter  or  Gooch  crucible,  wash 
well  with  hot  water,  dry  at  100°  C.,  and  weigh  as  BiOCl.  This 
weight  multiplied  by  0.801 8  will  give  that  of  the  bismuth. 

7.  In  the  absence  of  appreciable  amounts  of  antimony  the 
precipitation    by    hydrogen    sulphide    and    subsequent    washing 
with  ammonium  sulphide  may  be  omitted,  as  only  a  small  portion 
of  whatever  antimony  is    present    is  precipitated  with  the  bis- 
muth.    In  this  case  the  first  precipitate,  containing  the  bismuth 
and  a  little  lead,  may  be  at  once  redissolved  on  the  filter  with 
warm  dilute  nitric  acid  (1:4)  and' the  precipitation  repeated  on 
the  filtrate  as  described.     Copper,  silver,  arsenic,  and  such  amounts 
of  iron  as  occur  in  refined  lead  do  not  interfere 

8.  Bismuth  in  Lead  "  Bullion." — The  determination  of  bis- 
muth in  impure  lead  or  lead  bullion  may  be  carried    out  on 
the  same  lines  as  described  for  refined  lead.     From  10  to  25 
grams  may  be  taken,  according  to  the  presumed  or  known  nature 
of  the  material.     Antimony  may  usually  be  assumed  to  be  present. 
Proceed  with  the  determination  precisely  as  described  for  re- 
fined   lead  (6)   up  to  the  point  where    the  bismuth,  lead,  and 
antimony  sulphides  are  dissolved  in  hot  dilute  nitric  acid.     Now, 
instead  of  finishing  the  analysis  as  described,  it  is  best  to  repeat 


58  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  whole  series  of  operations  once  more.  In  this  way  the  impur- 
ities are  more  certain  to  be  removed  and  the  BiOCl  weighed 
pure. 

9.  Eakins's  Method  for  Bismuth  in  Refined  Lead.* — In  this 
method  for  the  determination  of  bismuth  in  refined  lead  and  lead 
bullion  the  bulk  of  the  lead  is  removed  at  the  outset  by  precipita- 
tion as  sulphate  from  the  nitric  acid  solution.     In  my  laboratory 
this  method  has  uniformly  given    low    results  as   compared  to 
those  obtained  by  the  method  of  Ledoux  &  Co.,  some  of  the 
bismuth  apparently  being    precipitated  with    the   lead.      For  a 
description   of    the   method  reference  is    therefore  made  to  the 
original  paper,  or  to  Furman's  Manual  of   Practical  Assaying, 
seventh  edition,  p.  193. 

10.  Volumetric  Method  for  Ores. — The  following  scheme  is 
based  on  Miller  and  Frank's  modification  of  Riderer's  method  :f 

Weigh  0.5  gram  of  the  ore  and  proceed  as  in  (i)  until  the 
washed  sulphides  of  bismuth,  etc.,  are  obtained  on  the  filter. 
Place  filter  and  precipitate  in  an  8-oz.  flask  and  heat  with  5-10  cc. 
of  1:1  nitric  acid  until  the  separated  sulphur  is  clean  and  the 
filter  well  disintegrated.  Dilute  a  little  and  then  filter  and  wash 
filter  thoroughly  with  i :  2  nitric  acid,  best  with  the  aid  of  a  filter- 
pump.  To  the  filtrate  add  30  cc.  of  a  cold  saturated  solution 
of  tartaric  acid,  then  drop  in  a  bit  of  litmus  paper  as  an  indicator 
and  make  the  solution  slightly  alkaline  with  potassium  hydroxide. 
Now  add  sufficient  potassium  cyanide  solution  to  dissolve  any 
precipitate  that  may  have  formed  (except  possibly  a  little  bismuth 
sulphide  thrown  down  by  sulphur  in  the  cyanide),  and  then 
pass  in  hydrogen  sulphide  gas  to  saturation.  Bismuth  sulphide 
is  precipitated;  copper,  arsenic,  antimony,  etc.,  remain  in  solu- 

*  Proceedings  Colorado  Scientific  Society,  Feb.  1895. 
t  Jour.  Am.  Chem.  Soc.,  XXV,  926. 


BISMUTH.  59 

tion.  Filter  and  wash  with  cold  water.  Dissolve  the  bismuth 
sulphide  in  dilute  nitric  acid  and  filter  the  solution  precisely  as 
described  above. 

1 1 .  The  filtrate  now  contains  the  bismuth  as  nitrate  together 
with  some  free  nitric  acid.     It  is  best  to  have  the  excess  of  the 
latter  about  5  per  cent.     Now  add  a  decided  excess  (3  or  4  times 
the  amount  theoretically  necessary  for  combining  with  all  the 
bismuth)  of  the  ordinary  molybdic  acid  solution  used  for  phos- 
phorus determinations  (xxn,  7).     There  should  be  no  precipitate 
produced  at  this  point.      Then  add  a  few  drops  of  Congo-red 
solution  (made    by  dissolving  i  part  of  Congo-red  in  100  parts 
of  30  per  cent,  alcohol)  and  slowly  run  in,  with  stirring,  very 
dilute  ammonia  from  a  burette.     A  white  precipitate  will  form, 
and  finally  the  indicator  will  become  pink.     Next  add  a  few 
drops  of  dilute  nitric  acid,  sufficient  to  change  the  color  to  lilac 
(just  neutral).     Now  dilute,  if  necessary,  to  about  200  cc.  and 
heat  slowly  on  a  thick  asbestos  pad,  very  hot  (60°  C.),  but  not 
to    boiling,    and    stir    vigorously.     The    precipitate    of   bismuth 
ammonium  molybdate   (BiNH4(MoO4)2)   should  coagulate  and 
appear  like  silver  chloride,  perhaps  colored  pink  by  the  indi- 
cator.        It   should   not   be  yellowish.     Filter  the  hot  mixture 
and  wash  the  precipitate  thoroughly  with  a  3  per  cent,  solution 
of  ammonium  sulphate.     If  the  above  directions  are  followed, 
the  precipitation  will  be  complete,  but  if  too  much  nitric  acid  is 
added,  so  that  the  indicator  is  turned  back  to  a  decided  blue 
color,  the  precipitate  does  not  collect  or  filter  as  well  and  the 
filtrate  may  contain  traces  of  bismuth.     If  the  precipitate  has  a 
yellow  color,  the  results  will  be  unreliable.     In  such  a  case,  make 
alkaline  with  ammonia,  then  add  nitric  acid  until  the  precipitate 
is  dissolved,  and  repeat   the  neutralization  and  heating.     It  is 
usually  unnecessary  to  add  more  ammonium  molybdate. 

12.  Make  a  mixture  of  75  cc.  of  water  and  15  cc.  of  strong 


60  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

sulphuric  acid.  Place  a  portion  of  this  in  a  beaker  and  rinse 
the  precipitate  into  it  from  the  filter  as  completely  as  possible. 
When  all  is  dissolved  pour  the  solution  through  the  filter  to 
dissolve  any  remaining  precipitate  and  wash  with  the  remainder 
of  the  acidulated  water.  Receive  the  filtrate  in  an'8-oz.  flask, 
add  5  grams  of  i  co-mesh  granulated  pure  zinc,  and  allow  to 
stand  until  the  solution  is  of  a  green  color  (not  brown)  and  the 
zinc  has  wholly  or  nearly  dissolved.  Now  place  a  thick  wad  of 
absorbent  cotton  in  a  funnel,  wet  it  and  place  a  little  granulated 
zinc  on  top.  Filter  the  reduced  solution  through  this  and  wash 
thoroughly  with  lukewarm  water.  Receive  the  filtrate  in  a 
somewhat  larger  flask,  which  has  been  filled  with  carbon  dioxide 
by  pouring  a  little  dilute  sulphuric  acid  over  some  sodium  acid 
carbonate  placed  in  the  bottom.  Warm  the  solution  to  about 
40°  C.  and  titrate  with  permanganate  solution,  the  same  that  is 
used  for  iron  determinations  (xv,  2),  as  described  in  xxn,  9. 

The  formula  BiNH4(NoO4)2,  indicates  that  2Mo  =  Bi,  and  it 
is  shown  in  xx,  n,  that  6Fe  =  2Mo;  therefore  6Fe  =  Bi,  or,  the 
iron  factor  of  the  permanganate  multiplied  by  0.6216  gives  tha 
bismuth  factor. 


CHAPTER  IX. 

CADMIUM. 

i.  Method  for  Ores. — To  0.5  gram  of  the  ore  in  an  8-oz.  flask 
add  10  cc.  of  strong  hydrochloric  acid  and  5  cc.  of  strong  nitric 
acid.  Boil  until  any  sulphides  present  are  decomposed  and  the  acid 
is  perhaps  half  expelled.  If  oxides  still  remain,  continue  to  heat 
with  addition  of  hydrochloric  acid  until  solution  is  as  complete  as 
possible.  Finally,  add  about  6  cc.  of  strong  sulphuric  acid 
and  boil,  best  over  a  free  flame,  until  fuming  copiously.  Cool,  add 
about  25  cc.  of  water,  heat  to  boiling,  and  allow  to  stand,  hot, 
for  a  short  time,  to  insure  the  solution  of  anhydrous  iron  sulphate, 
etc.  Then  cool,  filter  off  the  insoluble  residue  (including  any 
lead  sulphate),  and  wash  with  cold  dilute  sulphuric  acid  (1:10). 
.Dilute  the  filtrate  to  about  200  cc.  and  pass  in  hydrogen  sul- 
phide gas  to  saturation.  Filter  off  the  precipitated  sulphides  and 
wash  with  dilute  hydrogen  sulphide  water  slightly  acidulated 
with  hydrochloric  acid.  Rinse  the  precipitate  from  the  filter 
into  a  beaker  as  completely  as  possible,  using  no  more  water 
than  necessary,  place  the  beaker  under  the  funnel  and  pour 
through  the  filter  a  strong  cold  solution  of  pure  potassium  cya- 
nide. Agitate  the  beaker  so  as  to  mix  the  liquids  and  use  no  more 
cyanide  solution  than  necessary  to  dissolve  the  soluble  copper 
sulphide,  etc.,  that  may  be  present.  If  no  bismuth  or  lead  is 
present  (any  lead  should  have  been  practically  all  removed  as 
sulphate)  the  cadmium  sulphide  will  now  appear  yellow  or 

61 


62  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

orange.*  Filter  the  mixture  through  the  same  filter  as  before. 
If  it  runs  through  turbid  return  it  through  the  filter  until  clear. 
Wash  well  with  dilute  hydrogen  sulphide  water.  The  cadmium 
sulphide  has  a  tendency  to  pack  on  the  filter  and  impede  filtra- 
tion. If  possible,  wash  it  loose  each  time  and  the  washing  will 
then  proceed  much  more  rapidly.  If  the  washed  precipitate 
appears  appreciably  discolored,  indicating  bismuth,  proceed  as 
in  2,  below.  If  clean  and  yellow  or  orange,  dissolve  it  by  pour- 
ing through  the  filter  hot  dilute  (1:1)  hydrochloric  acid,  using 
as  little  as  possible.  If  the  volume  of  the  filtrate  is  not  too  large, 
receive  it  in  a  large  weighed  porcelain  crucible;  otherwise  col- 
lect it  in  a  beaker  and  transfer  it  to  the  crucible  in  small  portions 
at  a  time.  Place  the  crucible  and  contents  on  a  water-bath  and 
evaporate  the  solution  of  cadmium  chloride  to  complete  dryness. 
Now  cover  the  crucible  and  add  a  slight  excess  of  dilute  sulphuric 
acid.  When  spattering  has  ceased,  remove  and  rinse  off  the 
cover  and  continue  the  evaporation  as  far  as  possible  on  the 
water-bath.  Finally,  remove  the  excess  of  sulphuric  acid  by 
cautiously  heating  over  a  free  flame  until  no  more  fumes  are 
evolved.  Avoid  heating  higher  than  necessary.  It  is  best  to 
place  the  crucible  within  a  larger  one  fitted  inside  with  an  asbestos 
ring,  so  that  the  crucibles  do  not  touch.  Or,  the  crucible  may 
be  supported  on  a  clay  triangle  on  a  small  iron  sand-bath  contain- 
ing no  sand,  so  as  to  just  not  touch  the  bottom.  When  the 
fumes  have  ceased  to  come  off,  cool  and  weigh  the  crucible  and 
contents.  The  cadmium  sulphate,  CdSCU,  should  be  pure 
white  and  soluble  in  water  without  residue.  Its  weight  multi- 
plied by  0.5391  will  give  the  weight  of  the  cadmium,  from  which 
the  percentage  may  be  calculated. 

2.  If  f  e  cadmium  sulphide,  after  treatment  with  potassium 

*  When  precipitated  from  sulphuric  acid  solutions,  unless  very  weak  in  acid, 
the  cadmium  sulphide  is  orange-colored  rather  than  pure  yellow. 


CADMIUM.  £3 

cyanide,  appears  dark-colored,  bismuth  or  lead  (possibly  mer- 
cury) may  be  present.  Place  the  moist  precipitate  and  filter  in 
an  8-oz.  flask  and  add  10  cc.  of  strong  hydrochloric  acid  and  the 
same  amount  of  water.  Boil  the  mixture  until  the  cadmium 
sulphide  is  all  dissolved,  the  hydrogen  sulphide  expelled,  and 
the  filter  well  disintegrated.  Any  dark  insoluble  residue  appar- 
ently free  from  cadmium  may  be  neglected.  Dilute  with  25  cc. 
of  hot  water  and  filter,  washing  thoroughly  with  hot  water.  Dilute 
the  filtrate  somewhat,  add  sodium  carbonate  in  slight  excess 
and  then  i  or  2  grams  of  potassium  cyanide.  Digest  for  some 
time  at  a  gentle  heat  and  filter.  Wash  with  cold  water.  Bis- 
muth and  lead  remain  on  the  filter  as  carbonates.  Pass  hydrogen 
sulphide  through  the  filtrate,  diluted  if  necesary.  This  should 
precipitate  pure  yellow  cadmium  sulphide  unless  mercury  is 
present,  which  is  rarely  the  case.  Filter,  wash  with  hydrogen 
sulphide  water,  and  then  dissolve  in  hydrochloric  acid  and  finish 
as  described  above. 

3.  Electrolytic   Method.— Cadmium  can  be   separated   elec- 
trolytically  in  a  satisfactory  manner  from  its  solution  in  various 
electrolytes.     Its  alkaline  double-cyanide  solution  is  perhaps  as 
good  as  any,  if  not  the  best  electrolyte.     The  method  may  be 
applied  to  an  ore  as  follows: 

4.  Treat  i  gram  of  the  ore  by  the  methods  previously  de- 
scribed until  a  solution  of  the  chloride  or  sulphate  is  obtained, 
free  from  the  other  members  of  the  hydrogen  sulphide  group. 
The  solution  should  be  evaporated  if  necessary,  so  as  to  have 
the  volume  well  below  100  cc.     Add  a  drop  or  two  of  phenol  - 
phthalein  solution  and  then  pure  sodium  or  potassium  hydroxide 
solution   until   a   permanent   red   color  is   obtained.     Now  add 
cautiously  a  strong  solution  of  pure  potassium  cyanide  until  the 
precipitated  cadmium  hydroxide  is  completely  dissolved,  avoid- 
ing an  excess.     Dilute  to  100-125  cc.  and,  using  the  same  beaker 


64  TECHNICAL   METHODS   OF  ORE  ANALYSIS. 

and  electrodes  as  for  copper  (XITI,  10),  elcctrolyze  with  a  current 
of  ND  100=0.04  to  0.06  A.  and  ¥.=2.9-3.2.  Keep  the  solution 
at  a  temperature  of  about  60°  C.  In  from  4  to  6  hours  the  deposi- 
tion is  usually  complete.  Test  by  raising  the  level  of  the  liquid 
slightly  and  noting  if  any  deposition  occurs  on  the  clean  platinum 
surface  during  half  an  hour  or  so.  When  the  operation  is  ended, 
disconnect  and  remove  the  electrode,  wash  it  with  hot  water,  then 
with  alcohol,  and  finally  dry  it  at  100°  C.,  cool,  and  weigh. 

It  is  a  good  plan  to  replace  the  electrode  in  the  solution  and 
electrolyze  for  another  half  hour.  The  electrode  should  first  be 
cleaned  with  nitric  acid,  then  washed,  ignited,  and  again  weighed. 
If  desired,  the  solution  can  be  tested  with  hydrogen  sulphide. 
As  this  may  produce  a  yellow  color  in  the  cyanide  solution,  even 
in  the  absence  of  cadmium,  it  is  best  to  first  acidify  with  hydro- 
chloric acid  (under  a  hood)  and  then  heat  until  all  the  hydrocyanic 
acid  is  expelled. 

5.  Treadwell,*  using  the  same  electrolyte,  recommends  elec- 
trolyzing  in  the  cold  for  from  5  to  6  hours  with  a  current  of  0.5- 
0.7  ampere  and  an  electromotive  force  of  4.8-5  volts.     At  the 
end  of  this  time  the  current  is  increased  to  from  1-1.2  amperes 
and  the   solution  is  electrolyzed   for   i   hour  more.     Treadwell 
states  that  unless  the  current  is  increased  toward  the  end  of  the 
operation,  the  cadmium  will  not  be  all  deposited  at  the  end  of  1 2 
hours.     If  the  stronger  current  is  used  from  the  beginning,  some 
of  the  metal  is  liable  to  be  deposited  in  a  spongy  form,  resulting 
in  a  possible  loss  in  washing. 

6.  Smith  f    describes    the   deposition  of  cadmium   from  its 
sulphate  solution.     The  neutral  solution  is  acidified  with  3  cc. 
of  sulphuric  acid  of  1.09  sp.  gr.  and  diluted  to  125  cc.     Lily  G. 


*  Treadwell's  Analytical  [Chemistry  (Hall),  II,  2d  Ed.,  p.  166. 
f  Electrochemical  Analysis. 


CADMIUM.  65 

Kollock*  found  that  with  sach  a  solution,  maintained  at  65°  C., 
with  NDioo  =  0.078  ampere  and  volts -2.61,  the  deposition  was 
complete  in  5  hours.^ 

*  Jour.  Am.  Chem.  Soc.,  XXI,  925. 

f  See   Edgar  F.   Smith's  Electro-Analysis  for  rapid  method,   using  rotating 
electrode. 


CHAPTER  X. 

CALCIUM. 

i.  Ores,  etc. — The  calcium  is  usually  required  as  CaO. 
Treat  0.5  gram  of  the  ore  in  an  8-oz.  flask  with  whatever  acids 
are  best  suited  to  decompose  it.  Begin  ordinarily  with  10  cc. 
of  strong  hydrochloric  acid  and  heat  gently.  If  sulphides  are 
present,  add  5  cc.  of  strong  nitric  acid  (after  the  oxides  are 
dissolved)  and  boil  gently  until  decomposed.  If  the  decom- 
position is  perfect  sulphuric  acid  is  unnecessary,  but  with  ores 
I  usually  add  5  cc.  at  this  stage.  In  any  case  boil  until  most 
of  the  free  acid  is  expelled,  over  a  free  flame  if  sulphuric  acid 
has  been  used.  Now  cool,  if  necessary,  add  about  100  cc.  of 
water  and  5  cc.  of  strong  hydrochloric  acid,  heat  until  the  salts 
are  dissolved  and  then  filter  (never  omit  this  if  there  is  any  appre- 
ciable amount  of  insoluble  residue),  washing  with  hot  water. 
To  the  filtrate  add  2  cc.  of  a  saturated  solution  of  potassium 
dichromate  (this  may  be  omitted  if  lead  is  absent*),  15-20  cc. 
of  saturated  bromine  water  (to  precipitate  manganese),  and  then 
a  very  slight  excess  of  ammonia.  Cover  the  beaker  and  boil 
until  all  free  ammonia  is  expelled.  Allow  to  settle  somewhat 
and  then  filter  through  an  n-cm.  filter  and  wash  thoroughly  with 
hot,  dilute  ammonium  chloride  solution  (5  grams  to  500  cc.). 
If  lead  chromate  runs  through,  return  the  first  portions.  If  the 
precipitate  shows  much  manganese  it  is  always  well  to  test  the 

*  Lead  unquestionably  interferes,  although  but  slightly.  An  ore  containing 
30  per  cent,  lead  and  about  16  per  cent.  CaO  gave  results  about  0.25  per  cent, 
high  when  the  lead  was  not  removed.  Lead  may  also  be  removed  as  sulphide, 
as  described  in  xvu,  i. 

66 


CALCIUM.  67 

filtrate  by  adding  more  bromine  water  and  ammonia  and  boiling 
a  short  time.  If  any  manganese  comes  down,  filter  it  off,  it  being 
usually  unnecessary  to  expel  the  excess  of  ammonia  as  before. 
Wash  with  the  dilute  ammonium  chloride  solution. 

By  proceeding  as  above,  the  usual  double  precipitation  of  the 
iron  is  entirely  unnecessary.  The  usual  retention  of  lime  by  iron 
appears  to  be  due  to  the  formation  of  calcium  carbonate,  by  the 
absorption  of  carbon  dioxide  from  the  air  in  the  presence  of  free 
ammonia,  and  this  does  not  occur  if  the  ammonia  is  expelled 
previous  to  filtration.  A  neglect  to  filter  off  the  insoluble  residue 
before  the  iron  precipitation  will  usually  produce  a  low  result. 
I  am  unable  to  state  the  reason. 

2.  Make  the  filtrate  from  the  iron  strongly  ammoniacal,  heat 
to  boiling  and   add  an  excess  of  ammonium  oxalate  solution. 
This  should  be  added  in  sufficient  amount  to  convert  all  possible 
calcium   and   magnesium   to   oxalates    (the   magnesium   oxalate 
remaining  in  solution).     Thirty  cc.  of  a  saturated  solution  should 
be  sufficient  in  any  case.     It  is  best  to  dilute  it  somewhat  and  add 
it  boiling  hot.     Boil  the  mixture  about  10  minutes,  allow  to  stand 
hot  and  settle,  and  then  filter  through  an  n-cm.  filter  and  wash 
ten  times  with  hot  water. 

The  mode  of  procedure  now  depends  upon  whether  the  ore 
contains  much  or  little  magnesium.  In  the  former  case  the 
calcium  oxalate  is  almost  sure  to  contain  an  appreciable  amount 
of  magnesium  oxalate  and  should  therefore  be  purified.  Unless 
the  amount  of  magnesium  is  known  to  be  insignificant  it  is  always 
safest  to  proceed  as  follows: 

3.  Without  troubling  to  wash  the  precipitated  oxalate  more 
than  once,  rinse  it  from  the  filter  into  a  beaker.    What  little; 
remains  adhering  to  the  filter  may  usually  be  neglected  if  the 
same  filter  be  employed  for  the  next  filtration  of  the  oxalate. 


68  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Heat  the  mixture  in  the  beaker  and  then  dissolve  the  oxalates 
by  the  addition  of  as  little  hydrochloric  acid  as  possible.  Dilute 
to  about  50  cc.  with  hot  water,  make  alkaline  with  ammonia, 
and  add  about  10  cc.  of  the  ammonium  oxalate  solution.  Boil 
the  mixture  for  about  10  minutes,  allow  to  stand,  hot,  until 
settled,  and  then  filter  through  the  last  filter.  Wash  at  least  ten 
times  with  hot  water,  to  remove  every  trace  of  ammonium  oxalate. 
When  little  or  no  magnesium  is  present,  the  first  precipitate 
of  calcium  oxalate  will  be  sufficiently  pure  and  require  only 
thorough  washing  with  hot  water.* 

4.  In  a  400-cc.  beaker  prepare  a  mixture  of  5-7  cc.  of  strong 
sulphuric  acid  and  about  125  cc.  of  water.     Drop  the  filter  and 
precipitate   into  this  and  heat  to  about  70°  C.      Stir  to  effect 
the  decomposition  of  the  calcium  oxalate,  but  avoid  disintegrating 
the   filter.    Titrate   the   hot   solution  with   standard   potassium 
permanganate  solution.     Under  the  conditions  named  the  filter- 
paper  will  exercise  practically  no  influence  on  the  result,  and 
while  the  final  pink  tinge  will  gradually  fade,  there  will  be  no 
difficulty  in  noting  a  sharp  end-point.     Multiply  the  number 
of  cubic  centimeters  of  permanganate  required,  by  the  percentage 
value  in  CaO  of  i  cc.  to  obtain  the  per  cent,  of  CaO  in  the  ore. 

5.  The  permanganate  solution  used  for  iron  determinations 
(xv,  2)  will  serve  for  this  titration.     The  iron  factor  multiplied 
by  0.5017  will  give  the  CaO  factor.     This  is  because  the  same 
amount  of  oxygen  from  the  permanganate  is  required  to  oxidize 
the  oxalic  acid  in  the  calcium  oxalate  corresponding  to  i  mol. 
of  CaO,  as  is  required  to  oxidize  2Fe  from  the  ferrous  to  the 
ferric   condition.     That   is,    2Fe   are   equivalent   to    i    CaO   or 
1 1 1.8  parts  of  Fe  to  56.1  parts  of  CaO,  which  is  the  same  as 
i  part  Fe  to  0.5017  part  CaO. 

*  This  is  the  usual  practice  in  all  cases  in  ordinary  lead-smelter  work. 


CALCIUM. 


69 


6.  It  is,  however,  best  for  the  CaO  determination  to  stand- 
ardize   the    permanganate    directly    against    pure    oxalic    acid. 
Weigh  about  0.2  gram  of  the  crystals  and  dissolve  in  an  8-oz.  flask 
in  a  previously  prepared  mixture  of  5-7  cc.  of  strong  sulphuric 
acid  and  125  cc.  of  water.     Heat  to  about  70°  C.  and  titrate  to 
a  faint  pink  tinge  with  the  permanganate  solution.     The  first 
portion  of  permanganate  will  not  be  decolorized  instantly,  but 
when  once  the  decolorization  has  begun,  it  will  thereafter  occur 
quickly  until  the  end. 

Divide  the  weight  of  oxalic  acid  taken  by  the  number  of  cubic 
centimeters  required.  This  will  give  the  oxalic  acid  value  of  i  cc. 
of  the  permanganate.  Multiply  this  figure  by  0.445 1  to  obtain  the 
value  of  i  cc.  in  CaO,  expressed  in  grams.  This  last  factor  is 
obtained  as  follows:  56.1  parts  of  CaO  require  126.048  parts 
of  crystallized  oxalic  acid  to  form  calcium  oxalate.  Accordingly, 
i  part  of  oxalic  acid  is  equivalent  to  0.4451  part  of  CaO.  Of 
course,  in  the  CaO  determination  all  the  oxalic  acid  titrated  is 
derived  from  the  decomposition  of  the  calcium  oxalate  by  the 
sulphuric  acid. 

Having  determined  the  value  of  i  cc.  in  grams  of  CaO,  the 
percentage  value* on  the  basis  of  0.5  gram  of  ore  taken  is  easily 
calculated. 

Example. — Took  0.2163  gram  of  oxalic  acid.  Used  38.66  cc. 
of  permanganate.  0.2163^38.66  =  0.005594.  This  is  the  weight 
of  oxalic  acid  to  which  i  cc.  of  the  permanganate  is  equal.  Mul- 
tiplying by  0.4451  we  have  0.002491,  the  value  of  i  cc.  in  CaO, 
or  i  cc.  =0.4982  percent,  on  the  basis  of  0.5  gram  of  ore  taken. 

7.  Silicates    and    Substances    Not    Decomposed   by   Acids. — 
These  are  decomposed,   as  described   under  SILICA,   either  by 
immediate  fusion  with  alkali  carbonate  or  by  acid   treatment, 
followed  by  fusion  of  the  insoluble  residue.     The  nature  of  the 
substance  will  determine  these  points  precisely  as  in  the  case 


70  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

of  silica.  When  the  solution  eventually  obtained  contains  con- 
siderable silicic  acid,  it  is  best  to  render  it  insoluble  by  evapora- 
tion and  filter  it  off.  A  small  amount  of  silicic  acid  may  be 
neglected.  The  clear  hydrochloric  acid  solution  finally  obtained 
containing  all  the  calcium,  is  treated  as  described  above  (i). 

8.  "  Available  Lime  "  in  Ores  containing  Calcium  Fluoride. — 
Some  of   the  western  smelters  regard  the  calcium  contained  in 
calcium  fluoride  as  of  no  value  as  a  flux,  claiming  that  it  passes 
through   the   furnaces   unaltered,   without   combining   with    the 
fluxes  used.     In  paying  for  the  lime  in   an  ore,  only  that  which 
is  not  combined  with  fluorine  is  taken  into  consideration  and   is 
called  "available  lime."     The  method  used  for  determining  this 
portion  is  not  strictly  correct,  since  if    an  ore  contained  much 
calcium  sulphate  or  silicate,  at  least  some  of  the  CaO  thus  com- 
bined would  probably  fail  to  be  reported  as  "available."      As  a 
technical  method,  however,  in  regular  use,  it  is  sufficiently  satis- 
factory and  is  therefore  given  herewith. 

9.  Take  0.5  gram  of   the  ore  in  an  8-oz.  flask,  moisten  with 
water,  add  5  cc.  of  80  per  cent,  acetic  acid,  and  boil   nearly  to 
pastiness.     Take  up  in  about  30  cc.  of  equal  parts  of  80  per  cent, 
acetic  acid  and  water  and  boil  gently  for  a    few  minutes.     To 
remove  lead,  which  is  frequently  present,  add  2  cc.  of  a  saturated 
solution   of   potassium   dichromate   just   previous   to    this     last 
boiling.     Filter,  washing  with  hot  water.     To  the    filtrate  add 
about  20  cc.  of  saturated  bromine  water  and   then  (cautiously) 
make  alkaline  with  ammonia  and  heat  to  boiling.     It  is   gener- 
ally best  to  now  add  more  bromine  water  and  continue    the 
heating  for  a  short  time  to  make  sure  of  the  precipitation  of  all 
manganese.     Finally,   boil  off   all   the   free   ammonia,    rllow   to 
settle  somewhat,  and  filter  and  wash  as  in  the  regular  method  (i). 
Test  the  filtrate  for  unprecipitated  manganese  if  apparently  neces- 
sary, as  described  for  the  regular  method.     Make  the  final   filtrate 


CALCIUM.  71; 

strongly  ammoniacal,  heat  to  boiling,  precipitate  the  calcium  as 
oxalate,  and  finish  the  determination  exactly  as  described  for 
the  regular  method. 

This  will  give  all  the  CaO  contained  in  the  ore  as  carbonate 
and  also  as  sulphate  unless  the  Tatter  is  in  large  amount.  Calcium 
combined  as  fluoride  or  silicate  remains  practically  undissolved 
by  the  acetic  acid.  The  silicate  is  usually  small  in  amount 
and  the  calcium  so  combined  is,  in  fact,  regarded  as  no  more 
"available  "  than  that  existing  as  fluoride. 

10.  The  Percentage   of  Calcium  Fluoride    may    be    roughly 
determined  as  follows:    Ignite  the  undecomposed  residue  from 
the  acetic  acid  treatment  above,  together  with  the  filter,  in  a 
small  platinum  dish.     Cool,  add  a  little  strong  sulphuric  acid, 
and  heat  to  decompose  the  calcium  fluoride.     Finally  increase 
the  heat  so  as  to  expel  all  the  sulphuric  acid.     Cool  and  take 
up  in  10  cc.  of  strong  hydrochloric  acid.    Transfer  to  a  beaker, 
dilute  with  100  cc.  of  hot  water,  and  heat  to  boiling.     Filter  and 
determine  the  calcium  in  the  filtrate  in  the  usual  way.     It  is 
well  to  ignite  the  filter  and  residue  and  repeat  the  treatment  with 
sulphuric  acid  to  make  sure  that  the  fluoride  is  completely  decom- 
posed.    This  portion  may  be  precipitated  separately  and  any 
calcium   oxalate  obtained  eventually  united  to   the   main    por- 
tion.    The  CaO  found  must  be  calculated  to  CaF2.    56.1  CaO  = 
78.1  CaF2.     (See  Kneeland's  method,  xiv,  i.) 

11.  Rapid  Volumetric  Determination  of  CaO    in  Limestone, 
Cement,  Lime,  Blast-furnace  Slags,  etc.*— The  following  rapid 
method  for  the  determination  of  CaO  is  applicable  to  miterials 
in  which  the  calcium  is  present  either  as  oxide,  carbonate,  or 
silicate,  and  is  dependent  on  the  fact  that  calcium  can  be  com- 
pletely precipitated  as  oxalate  in  solutions  containing  free  oxalic 
acid,  while  iron,  aluminum,  and  magnesium  are  not. 

*  From  paper  by  Richard  K.  Meade,  Chemical  Engineer,  Vol.  i,  p.  20. 


72  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

12.  Decomposition  of  the  Sample.— For  high-grade  lime- 
stones, that  is,  those  which  when  burned  do  not  give  a  hydraulic 
lime,  weigh  0.5  gram  into  a  platinum  crucible  cover  and  ignite 
for  5  minutes  over  a  Bunsen  burner,  and  then  for  5  minutes  over 
the  blast-lamp.  This  heating  must  be  cautiously  carried  out> 
as  magnesian  stones  are  likely  to  fly  out  if  heat  is  applied  too 
suddenly.  Start  the  ignition  over  a  low  Bunsen  flame  and  grad- 
ually raise  until  the  full  heat  is  attained,  then  continue  for  5 
minutes  and  follow  with  a  blast-lamp.  Empty  the  contents  of 
the  crucible  into  a  500-0:.  beaker  and  add  40  cc.  of  dilute  (1:1) 
hydrochloric  acid;  heat,  and  when  solution  of  the  sample  is 
complete  proceed  as  in  13. 

For  cement  rock  or  hydraulic  limestones,  weigh  the  sample  as 
before  and  carefully  mix  with  it  J  gram  of  finely  ground  sodium 
carbonate  by  stirring  with  a  glass  rod.  Brush  off  the  rod  into 
the  crucible  and  ignite  over  a  Bunsen  burner,  starting  with  a 
low  flame  and  gradually  raising  it  until  the  full  heat  is  attained. 
Continue  heating  for  5  minutes  longer  and  then  ignite  over  the 
blast  for  the  same  length  of  time.  Place  the  crucible  in  a  500-0:. 
beaker  and  decompose  the  sintered  mass  in  the  crucible  with 
40  cc.  of  dilute  (1:4)  hydrochloric  acid,  keeping  the  beaker 
covered  to  avoid  loss  by  effervescence.  Heat  until  solution  is 
complete  and  proceed  as  in  13. 

For  cement,  pass  the  sample  through  a  loo-mesh  screen,  weigh 
0.5  gram  into  a  dry  500- cc.  beaker  and  add,  with  constant  stirring, 
20  cc.  of  water.  Break  up  the  lumps,  and  when  all  the  sample 
is  in  suspension  except  the  heavier  particles,  ado!  20  cc.  of  dilute 
(i  :i)  hydrochloric  acid  and  heat  until  solution  is  complete.  This 
usually  takes  5  or  10  minutes.  Proceed  as  in  13. 

Many  slags  are  soluble  in  concentrated  hydrochloric  acid. 
When  this  is  the  case,  weigh  0.5  gram  into  a  5oo-cc.  beaker, 
stir  up  with  a  very  little  water  and  add  20  cc.  of  strong  hydro- 


CALCIUM. 


73 


chloric  acid  and  heat.     When  solution  is  complete  proceed  as 
in  13. 

13.  The     Determination.  —  Carefully    add    dilute    ammcnia 
(sp.  gr.  0.96)  to  the  solution  of  the  sample  until  a  slight  perma- 
nent precipitate  forms.     Heat  to  boiling  and  add  10  cc.  of  a  10 
per  cent,  solution  of  oxalic  acid.     Stir  until  the  iron  and  alu- 
minum hydroxides  are  entirely  dissolved  and  only  a  slight  pre- 
cipitate of  calcium  oxalate  remains.     Now  add  200  cc.  of  boiling 
water  and  sufficient   (20  cc.)   saturated  solution  of  ammonium 
oxalate  to  precipitate  the  calcium.     Boil  and  stir  for  a  few  moments, 
remove  from  the  heat,  allow  the  precipitate  to  settle,  and  filter 
on  an  n-cm.  filter.     Wash  the  precipitate  and  paper  10  times 
with  hot  water,  using  not  more  than  10  or  15  cc.  of  water  each 
time.      Remove  the  filter  from  the  funnel,  open  and  lay  against 
the  sides  of  the  beaker  in  which  the  precipitation  was  made,  wash 
from  the  paper  into  the  beaker  with  hot  water,  add  dilute  sul- 
phuric acid  (4),  fold  the  paper  over  and  allow  to  remain  against 
the  walls  of  the  beaker.     Heat  to  80°  C.  and  titrate  with  standard 
potassium   permanganate    (5)    until   a  pink   color  is   obtained; 
now  drop  in  the  filter-paper,  stir  until  the  color  is  discharged, 
and  finish  the  titration  carefully,  drop  by  drop. 

14.  The  permanganate  is  best  standardized  for  this  deter- 
mination by  means  of  pure  calcite  or  Iceland  spar,  as  this  does 
away  with  uncertain  factors  and  also  with  the  error  introduced 
by  the  solubility  of  calcium  oxalate.     The  procedure,  which  is  as 
follows,  is  that  recommended  by  the  Committee  of  the  Lehigh 
Valley  Section  of  the  American  Chemical  Society: 

Make  up  potassium  permanganate  solution  by  taking  6  grams 
of  the  salt  to  i  liter  of  water;  let  stand  a  few  days  before  standard- 
izing. 

Weigh  out  0.5  gram  of  powdered  calcite  into  a  4oo-cc.  beaker; 
add  100  cc.  of  water  and  10  cc.  of  hydrochloric  acid  (1:1);  boil 


74  TECHNICAL  METHOD.  OF  ORE    ANALYSIS. 

gently  until  all  carbon  dioxide  is  expelled,  and  when  completely 
dissolved  make  alkaline  with  ammonia  and  add,  little  by  little, 
20  cc.  of  boiling-hot  saturated  solution  of  ammonium  oxalate; 
continue  boiling  for  5  minutes;  let  settle,  filter,  wash,  transfer 
precipitate  to  original  beaker  (13);  dissolve  in  dilute  sulphuric 
acid  and  titrate  with  the  permanganate  as  in  the  determination 
of  calcium. 

15.  Notes  on  the  Foregoing  Method. — In  this  method  lead 
appears  to  interfere  more  or  less,  bringing  the  results  high ;  it  is 
therefore  not  so  suitable  for  ores  in  general  as  the  longer  method 
first  given. 

In  neutralizing  with  ammonia  it  is  best  to  neutralize  nearly 
all  the  free  and  combined  acid,  and  the  ammonium  oxalate  added 
later  should  be  in  sufficient  excess  to  complete  this  neutralization 
of  the  mineral  acid. 


CHAPTER  XI. 

CHLORINE. 

i.  Mohr's  Volumetric  Method. — The  chloride  solution  should 
be  cold  and  neutral.  If  acid,  it  should  be  neutralized  with  pure 
sodium  or  calcium  carbonate  in  slight  excess.  To  the  cold 
neutral,  or  faintly  alkaline  solution  contained  in  a  porcelain 
casserole  or  evaporating-dish  add  i  cc.  of  a  2  per  cent,  solution 
of  neutral  potassium  chromate.  Titrate  with  a  N/io  solution 
of  silver  nitrate  until  a  permanent  faint-red  tinge  is  obtained, 
due  to  the  formation  of  silver  chromate.  This  compound  cannot 
exist  permanently  in  the  mixture  until  all  the  chlorine  has  been 
precipitated  as  silver  chloride.  The  mixture  should  be  well 
stirred  after  each  addition  of  silver  nitrate,  which  toward  the 
last  should  be  added  only  drop  by  drop.  As  the  faint  reddish 
tinge  is  somewhat  difficult  to  distinguish,  various  schemes  have 
been  proposed  to  facilitate  its  detection.  I  have  found  it  a  good 
plan,  when  the  end-point  is  apparently  attained,  after  reading 
the  burette,  to  pour  off  half  the  liquid  into  a  similar  casserole 
and  then  add  i  more  drop  of  the  silver  nitrate  solution  to  one 
casserole  and  note  if  the  two  portions  of  the  liquid  now  show 
any  difference.  When  such  a  difference  can  be  detected,  the 
end-point  has  certainly  been  reached  and  it  is  usually  safe  to 
accept  the  reading  of  the  burette  taken  previous  to  the  last  drop. 
For  accurate  work  a  blank  test  should  be  made  on  the  same 

75 


76  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

volume  of  liquid  to  see  how  much  silver  solution  is  required 
to  produce  a  tint  when  no  chloride  is  present,  and  this  amount 
must  be  deducted  from  that  used  in  the  analysis.  Multiply 
the  number  of  cubic  centimeters  used  by  0.003545  to  obtain  the 
weight  of  the  chlorine  present,  or  by  0.00585  for  the  weight  of 
the  corresponding  sodium  chloride. 

2.  The  standard  N/io  silver  nitrate  solution  for  the  above 
titration  may  be  prepared  as  follows:  Heat  pure  silver  nitrate 
to  120°  C.  for  10  minutes,  then  cool  and  weigh  16.994  grams, 
dissolve  in  water  and  dilute  to  i  liter,  i  cc.  =  0.003545  gram  of 
chlorine,  or  0.00585  gram  of  sodium  chloride.  Of  course  any 
other  weight  of  silver  nitrate  can  be  taken  and  the  corresponding 
value  of  the  solution  obtained  by  calculation. 


CHAPTER  XII. 

CHROMIUM. 

METHODS  are  given  below  for  the  determination  of  chromium 
in  iron  ores,  chrome-iron  ore,  and  steel.  These  will  include 
most  of  the  cases  likely  to  be  met  by  the  metallurgical  chemist. 

i .  Method  for  Iron  Ores  with  Small  Amounts  of  Chromium.* 
— Fuse  i  gram  of  the  very  finely  ground  ore  with  a  mixture  of 
5  grams  of  sodium  carbonate  and  0.5  gram  of  potassium  nitrate 
in  a  platinum  crucible  or  small  dish.  After  fusion,  extract  the 
melt  with  hot  water  and  transfer  the  mixture  to  a  small  beaker. 
If  the  solution  is  colored  by  manganese,  add  a  little  alcohol  and 
warm  the  mixture.  This  will  precipitate  the  manganese  as 
dioxide.  Allow  the  precipitate  to  settle  and  note  the  color  of 
the  clear  solution.  If  chromium  is  present  it  will  be  more  or 
less  yellow.  If  quite  colorless,  chromium  may  be  considered 
absent.  Filter  the  mixture,  washing  with  water,  and  dry  and 
ignite  the  insoluble  residue  on  the  filter.  Now  grind  it  with 
ten  times  its  weight  of  sodium  carbonate  and  a  little  potassium 
nitrate,  fuse  the  mixture  and  extract  with  water,  etc.,  as  before. 
Filter  and  add  the  filtrate  to  the  former  one.  Acidify  the  com- 
bined filtrates  with  hydrochloric  acid  and  evaporate  to  dryness 
to  render  the  silica  insoluble  and  reduce  the  chromic  acid  to 
Cr2O3.  Take  up  in  hydrochloric  acid,  dilute,  and  filter.  Pre- 

*  Mainly  from  Blair.     Chemical  Anal,  of  Iron. 

77 


78  TECHNICAL  METHODS   OF   ORE  ANALYSIS. 

cipitate  the  Cr2O3  and  A12O3  in  the  filtrate  with  ammonia.  Boil 
for  a  short  time,  filter,  and  wash  well  with  hot  water.  Dry  and 
ignite  the  precipitate  and  then  fuse  it  with  as  little  sodium  car- 
bonate and  potassium  nitrate  as  possible.  Extract  the  melt 
with  water  and  transfer  the  mixture  to  a  platinum  dish.  Evap- 
orate the  liquid  until  it  is  very  concentrated,  adding  crystals  of 
ammonium  nitrate  from  time  to  time  to  change  all  the  carbonated 
and  caustic  alkali  to  nitrate.  Each  addition  of  the  ammonium 
nitrate  produces  an  effervescence  and  ammonium  carbonate 
is  given  off.  The  solution  finally  becomes  almost  syrupy  and 
smells  faintly  of  ammonia,  the  addition  of  ammonium  nitrate 
no  longer  causing  an  effervescence.  Now  add  a  few  drops  of 
ammonia  and  filter  from  the  precipitated  alumina,  aluminum 
phosphate,  manganese  dioxide,  etc.  The  filtrate  contains  the 
chromium  as  alkali  chromate.  Add  an  excess  of  a  strong  solu- 
tion of  sulphur  dioxide,  which  changes  the  color  of  the  solution 
from  yellow  to  green.  Boil  well,  add  an  excess  of  ammonia, 
boil  again  for  a  few  minutes,  filter  on  an  ashless  filter,  and  wash 
thoroughly  with  hot  water.  Dry  and  ignite  the  precipitate  and 
weigh  as  Cr2O3.  Multiply  the  weight  by  0.6846  to  obtain  that 
of  the  chromium. 

2.  Method  for  Chrome  Iron  Ore. — Grind  the  ore  in  an  agate 
mortar  to  the  finest  possible  powder.  Weigh  0.5  gram  into  a 
nickel  or  copper  crucible  of  about  2o-cc.  capacity,  in  which  have 
previously  been  placed  3  or  4  grams  of  sodium  peroxide.  In 
taking  the  sodium  peroxide  from  the  bottle  or  can,  reject  any 
white  crust  on  top,  which  consists  mainly  of  carbonate  and  oxide, 
and  select  only  the  yellow  material.  Thoroughly  mix  the  contents 
of  the  crucible,  and  then  heat  gently  over  a  Bunsen  burner  turned 
very  low  until  the  mass  is  entirely  liquid.  This  may  take  about 
10  minutes.  Keep  in  a  condition  of  low  redness  for  about 
10  minutes.  Allow  to  cool  until  a  crust  forms  on  top  and  then 


CHROMIUM.  79 

add  i  gram  more  of  sodium  peroxide  and  fuse  again  at  low  red- 
ness for  about  5  minutes.  Cool,  place  the  crucible  and  contents 
in  a  porcelain  dish,  add  50-100  cc.  of  water,  and  heat  for  a  few 
minutes  until  the  mass  is  dissolved.  Remove  and  rinse  off  the 
crucible.  If  the  solution  is  purple  add  a  little  more  sodium 
peroxide.  Boil  the  covered  solution  for  10  minutes  to  decompose 
the  sodium  peroxide,  since  if  any  of  the  latter  were  allowed  to 
remain  it  would,  when  the  solution  was  subsequently  acidified, 
react  on  the  chromate  and  reduce  the  chromium  to  Cr2Os.  The 
solution  is  now  so  strong  in  sodium  hydroxide  that  it  would 
probably  rot  a  filter  unless  very  largely  diluted.  To  avoid  the 
dilution  the  sodium  hydroxide  may  be  partially  changed  to  car- 
bonate by  the  addition  of  ammonium  carbonate,  but  this  must 
not  be  done  until  the  sodium  peroxide  has  been  decomposed 
by  boiling,  as  otherwise  some  ammonium  nitrite  would  be  formed 
which  would  cause  a  low  result.  Therefore,  after  the  boiling, 
add  5  grams  of  ammonium  carbonate,  which  should  be  sufficient 
to  neutralize  about  four-fifths  of  the  sodium  hydroxide  present, 
still  leaving  an  excess  of  the  latter.  As  soon  as  the  ammonium 
carbonate  has  dissolved  the  liquid  is  ready  for  filtration.  Filter 
off  the  insoluble  material  and  wash  it  thoroughly,  receiving  the 
filtrate  in  a  large  beaker.  Treat  the  residue  remaining  on  the 
filter  with  hydrochloric  acid.  If  any  of  it  proves  to  be  insoluble 
it  may  be  undecomposed  ore  and  it  should  be  fused  again  with 
sodium  peroxide. 

3 .  Acidify  the  filtrate  with  dilute  sulphuric  acid  (1:4)  and 
then  add  a  considerable  excess — 25  cc.  or  more.  Allow  the  solu- 
tion to  cool  and  then  transfer  to  a  battery-jar  (such  as  that  used 
for  iron  titrations,  xv,  7)  and  dilute  to  700  cc.  with  cold  water. 
Now  add  a  weighed  amount  of  ferrous  ammonium  sulphate  which 
is  more  than  sufficient  to  reduce  the  chromium  present.  To 
do  this,  place  a  sufficient  quantity  of  the  salt  in  a  weighing-bottle 


So  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

/ 

and  carefully  weigh  the  whole;  then  add  the  salt  in  small  por- 
tions to  the  chromium  solution,  while  stirring,  until  the  yellow 
color  of  the  chromic  acid  has  entirely  disappeared,  and  also  until 
a  blue  test  is  obtained  when  a  drop  of  the  solution  is  removed  and 
touched  with  a  drop  of  a  weak  potassium  ferricyanide  solution. 
Now,  without  delay,  titrate  the  excess  of  ferrous  iron  salt  with 
standard  potassium  permanganate,  and  then  again  weigh  the 
bottle  of  ferrous  ammonium  sulphate  to  determine  the  amount 
used.  The  weight  of  ferrous  ammonium  sulphate  consumed 
in  reducing  the  chromic  acid  is  thus  found,  from  which  the 
corresponding  weight  of  the  chromium  or  Cr2Os  may  be  calcu- 
lated. 

4.  The  regular  permanganate  solution  used  for  iron  may  be 
employed  for  the  titration.  It  is  best  to  standardize  it  for  this 
titration  directly  against  ferrous  ammonium  sulphate.  Weigh 
out  portions  of  about  1.5  grams  each  of  the  salt  and  dissolve  in 
a  battery- jar  in  700  cc.  of  cold  water  containing  10  cc.  of  strong 
sulphuric  acid.  Titrate  at  once  to  a  pink  tint.  Also  run  a  blank 
to  determine  the  correction  required  for  the  water  and  acid 
(see  xv,  n). 

The  value  of  i  cc.  of  the  permanganate  in  ferrous  ammonium 
sulphate  is  thus  found. 

167.7  Parts  of  ferrous  iron  are  required  to  reduce  52.1  parts 
of  chromium  in  chromic  acid  to  Cr2Os,  or  i  part  Fe  — 0.3107 
parts  Cr.  The  ferrous  ammonium  sulphate  contains  14.25  per 
cent,  of  ferrous  iron;  therefore  i  part  of  the  salt  =  0.0442 7  part 
of  Cr. 

Having  found  by  the  titration  the  excess  of  ferrous  ammo- 
nium sulphate  and  deducted  this  from  the  total  amount  of  the 
salt  used,  the  weight  of  the  remainder  multiplied  by  0.04427 
will  give  the  weight  of  the  chromium  sought,  or,  if  multiplied 
by  0.06468,  the  weight  of  the  Cr2Os. 


CHROMIUM.  8 1 

5.  Method  for  Steel.*— This  method  is  based  upon  the 
well-known  fact  that  chromic  salts  can  be  oxidized  completely 
to  chromic  acid  by  the  addition  of  potassium  chlorate  to  a  con- 
centrated nitric  acid  solution,  and  the  fact  also  that  the  presence 
of  nitric  acid  does  not  interfere  with  the  titration  of  chromic 
acid  in  a  cold  solution  by  means  of  ferrous  sulphate  and  per- 
manganate. 

Weigh  3  grams  of  steel  into  a  4oo-cc.  flask,  add  35  cc.  of  strong 
hydrochloric  acid,  and  boil  for  5  or  10  minutes,  which  will  be 
found  sufficient  to  dissolve  completely  even  the  highest  chrome- 
steels.  When  most  of  the  hydrochloric  acid  is  boiled  off,  add 
150  cc.  of  strong  nitric  acid  and  continue  the  boiling  until  no 
more  brown  fumes  are  seen  at  the  mouth  of  the  flask,  showing 
that  the  hydrochloric  acid  has  all  been  driven  off.  Remove  the 
flask  from  the  flame  or  hot  plate,  allow  to  cool  for  2  or  3  minutes, 
and  then  add  10  grams  of  potassium  chlorate  in  crystals.  It  is 
best  to  allow  the  solution  to  cool  somewhat  before  adding  the 
chlorate  •  in  order  to  dimmish  the  violence-  of  the  effervescence 
due  to  the  action  of  the  chlorate  on  the  chromic  salts.  Replace 
on  the  hot  plate  and  boil  down  to  about  40  cc.  in  order  to  com- 
pletely decompose  the  potassium  chlorate.  It  is  necessary  to 
decompose  the  chlorate  completely  or  results  will  be  from  o.i 
to  0.2  per  cent  high,  but  the  amount  of  nitric  acid  left  in  the 
solution  is  unimportant.  At  this  stage  the  chromium  will  all  be 
in  the  solution  in  the  form  of  chromic  acid.  Any  manganese 
will  be  precipitated  as  dioxide,  and  generally  some  crystals  of 
potassium  nitrate  arising  from  the  decomposition  of  the  chlorate 
will  have  separated  out.  Add  100  cc.  of  water  and  a  few  drops 
of  hydrochloric  acid.  This  will  at  once  dissolve  the  manganese 
dioxide  without  action  on  the  chromic  acid.  Boil  the  solution 

*  From  paper  read  by  A.  G.  McKenna  before  the  Chemical  Section  of  the 
Engineers'  Society  of  Western  Pennsylvania,  June  18,  1896. 


82  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

for  a  few  minutes  to  remove  the  chlorine  set  free  by  the  reduction 
of  the  manganese  dioxide  and  then  cool  to  room  temperature. 
Make  the  cold  solution,  contained  in  a  battery-jar,  up  to  700  cc. 
with  cold  water  and  add  a  weighed  excess  of  ferrous  ammonium 
sulphate,  as  described  in  3,  above.  Finally,  titrate  the  excess 
of  ferrous  salt  with  permanganate  and  calculate  the  result  as 
in  4. 

In  very  many  chrome-steels  the  amount  of  manganese  is  so 
inappreciable  in  comparison  with  the  chromium  that  for  practical 
results  it  is  not  necessary  to  dissolve  the  dioxide  as  described 
above,  but  the  solution  after  the  evaporation  to  40  cc.  may  be 
diluted  and  titrated  at  once. 

5.  Rapid  Method  for  the  Determination  of  Chromium  in 
Chrome  and  Chrome-nickel  Steel.* — Dissolve  i  gram  of  the  steel 
by  warming  in  a  large  covered  beaker  with  25  cc.  of  the  acid 
mixture  described  below.  When  solution  is  complete  remove 
from,  the  heat  and.  add  about  15  or  20  cc.  of  cold  water.  Rotate 
the  liquid  in  the  beaker  and  drop  in  at  once,  about  i  gram  of 
sodium  bismuthate  and  continue  to  rotate  the  mixture  for  a 
few  seconds.  Now  heat  to  boiling  and  boil  rapidly.  The 
permanganate  formed  by  the  sodium  bismuthate  will  be  rapidly 
decomposed  and  there  will  remain  a  clear  violet  liquid  (man- 
ganic metaphosphate).  Further  boiling-  will  complete  the  con- 
version of  the  chromium  to  CrOa. 

Decompose  the  excess  of  manganic  metaphosphate  with  one- 
half  cc.,  or  more  if  necessary,  of  dilute  hydrochloric  acid  and  boil 
one  minute.  Cool  somewhat,  dilute  to-  200  cc.  with  cold  water, 
add  a  slight  excess,  of  ferrous  ammonium  sulphate  (as  in  3)  and 
titrate  with  permanganate.  Calculate,  the  result  as  in  4. 

The  end-reaction  is  very  sharp,  the  results  are  accurate  and 

*  N.  M.  Randall,  Mining  Science,  LXI,  56. 


CHROMIUM.  83 

an  analysis  can  be  completed  in  10  minutes.     The  method  has 
not  yet  been  tested  in  presence  of  tungsten  and  molybdenum. 
Acid  mixture  for  dissolving  the  steel: 
300  cc.  nitric  acid,  1.42  sp.  gr. 
300  cc.  sulphuric  acid,  i  part  acid,  3  parts  water. 
300  cc.  water. 

100  cc.  phosphoric  acid,  85  per  cent, 
ij  grams  manganese  sulphate. 


CHAPTER  XIII. 

COPPER. 

DURING  the  many  years  that  the  iodide  method  for  copper 
has  been  used  in  my  laboratory  it  has  been  constantly  studied, 
and  from  time  to  time  slightly  modified,  until  it  is  now  the  most 
accurate  practical  method  for  ores  with  which  I  am  acquainted. 

While  the  accuracy  of  the  electrolytic  method  cannot  perhaps 
be  exceeded,  the  electrolytic  method  as  actually  carried  out 
in  some  laboratories  is  liable  to  give  erroneous  results,  principally 
owing  to  the  failure  to  remove  interfering  impurities  found  in 
many  ores.  The  proper  removal  of  these  impurities  is  apt .  to 
be  quite  tedious  and  involve  considerable  manipulation,  tending 
to  cause  loss.  I  therefore  give  the  iodide  method  the  preference 
in  most  cases  as  being  more  practical  and  nearly  if  not  quite  as 
accurate  as  the  electrolytic  at  its  best. 

i.  Iodide  Method.* — A  standard  solution  of  sodium  thio- 
sulphate  is  required.  Make  up  a  solution  containing  about 
19.5  grams  of  the  pure  crystals  to  the  liter.  Standardize  this  as 
follows:  Weigh  carefully  about  0.2  gram  of  pure  copper- foil 
and  place  in  an  8-oz.  flask  (Whitall  Tatum  Co.,  pear-shaped). 
Addx  best  from  a  small  pipette,  5  cc.  of  strong  nitric  acid  (sp.  gr. 
1.42)  which  will  quickly  dissolve  the  copper.  Dilute  the  solution 
a  little  and  boil  to  expel  the  red  fumes.  Now  dilute  to  about 
40  cc.  and  add  ammonia  in  slight  excess.  Again  boil  until  the 
ammonia  odor  is  faint  and  then  add  a  marked  excess  of  80  per 
cent,  acetic  acid  and  continue  the  boiling  for  about  a  minute 

*  Author's  modification. 

84 


COPPER.  85 

longer.  This  last  boiling  is  important,  as  it  effects  the  neutrali- 
zation or  -expulsion  of  any  remaining  oxidizing  compounds  that 
would  cause  a  return  of  the  blue  color  after  titration.  See  that 
no  copper  salt  remains  undissolved.  Cool  to  room  temperature 
and  add  6  cc.  of  a  50  per  cent,  solution  of  potassium  iodide, 
or  3  grams  of  the  solid.  Cuprous  iodide  will  be  precipitated 
and  iodine  liberated  according  to  the  reaction, 


2(Cu.2C2H3O2)  +4KI  =  Cu2I2+4(K.C2H3O2)  +2!. 

The  free  iodine  colors  the  mixture  brown.  Titrate  at  once 
with  the  thiosulphate  solution  until  the  brown  tinge  has  become 
fa'int  and  then  add  sufficient  starch  solution  to  produce  a  marked 
blue  coloration.  Continue  the  titration  cautiously  until  the 
last  faint  lilac  tint  is  entirely  removed  by  a  single  drop.  In  the 
case  of  an  ore  the  presence  of  lead  or  bismuth  may  change  the 
color  of  the  final  tint,  but  the  end-point  is  equally  sharp,  espe- 
cially if  the  last  few  .drops  of  thiosulphate  are  allowed  to  fall 
into  the  center  of  the  slowly  rotating  liquid,  and  any  change 
from  the  surrounding  surface  noted.  (_  One  cc.  of  the  thiosulphate 
solution  will  be  found  to  correspond  to  about  0.005  gram  of 
copper,  or  about  i  per  cent,  in  the  case  of  an  ore  where  0.5  gram 
has  been  taken  for  assay.  The  reaction  between  the  thiosul- 
sulphate  and  the  iodine  is 


2(Na2S2O3)  +  2l  =  2NaI+Na2S4O6. 

Sodium  iodide  and  tetrathionate  are  formed.  The  thio- 
sulphate solution  made  from  the  pure  crystals  and  distilled  water 
is  quite  stable.  There  is  usually  a  slight  decomposition  during 
the  first  24  hours,  due  to  the  action  of  dissolved  carbon  dioxide 
or  oxygen  in  the  water,  but  after  this  period  the  solution  will 
remain  practically  unchanged  indefinitely  if  kept  in  a  bottle  of 


86  TECHNICAL  METHODS  OF    ORE   ANALYSIS. 

amber  glass  or  in  the  dark.     In   my  experience,  actinic  light 
appears  to  be  the  only  active  decomposing  agent  of  consequence. 

2.  Starch  Solution. — The  following  solution  is  the  result  of 
personal  experiment:    Make  a  cold  saturated  solution  of  com- 
mercial  sodium   chloride   in   distilled   water  and   filter  it.     To 
500  cc.  of  this  solution  add  100  cc.  of  80  per  cent,  acetic  acid 
and  3  grams  of  starch.     Mix  cold.    Boil  until  nearly  clear;  about 
two  minutes.     Add  a  little  water  to  replace  that  lost  by  boil- 
ing, perhaps  25  cc.     A  true  solution  of  all  the  starch  is  thus 
obtained.     No  filtering  or  settling  is  required  and  the  solution 
may  be  cooled  and  used  at  once.     It  keeps  indefinitely  and  gives 
sharper  end-points  than  the  ordinary  starch  liquor. 

3.  Treatment  of  an  Ore. — To  0.5  gram  of  the  ore  in  an  8-oz. 
flask  add  10  cc.  of  strong  hydrochloric  acid  and  5  cc.  of  strong 
nitric  acid.     Boil  until  decomposition  is  complete,  using  more 
of  the  acids  if  necessary   (and  enough  at  the  end  to    hold  all 
soluble  salts  in  solution),  and  then  add  8  cc.  of  strong  sulphuric 
acid  and  boil  to  abundant  fumes,  best  over  a  free  flame,  but  do 
not  boil  off  much  of  the  sulphuric  acid.*     After  cooling,  boil 
with  about  30  cc.  of  water  for  a  moment  and    then  allow  to 
stand,    hot,    until   any   anhydrous    ferric   sulphate   has    entirely 
dissolved;    then  filter  through  a  p-cm.   filter  to  remove  more 
especially  any  lead  sulphate.     Receive  the  filtrate  in  a  beaker 
about  6-cm    in  diameter.     Wash  the  filter  and  residue  at  least 
six  times  with  hot  water.     The  final  volume  of  the  filtrate  will 
ordinarily  not  much  exceed  75  cc.     Place  in  the  beaker  a  piece 
of  aluminum  prepared  as  follows:    Cut  a  strip  of  stout  sheet 
aluminum  2.5  cm.  wide  and  about  14  cm.  long  and  bend  this 
into  a  triangle  so  it  will  stand  on  its  edge  in  the  beaker.     The 
same  aluminum  may  be  used  repeatedly  as  it  is  but  little  attacked 

*  If  impure  sulphur  separates,  it  is  best  cleaned  by  allowing  the  strong  sul- 
phuric acid  to  continue  just  at  a  boil  (so  as  not  to  evaporate  much)  for  some  time. 


COPPER.  87 

each  time.  Cover  the  beaker  and  heat  to  boiling.  Allow  to 
boil  from  7  to  10  minutes,  which  should  be  sufficient  to  precipi- 
tate all  the  copper  in  any  case,  provided  the  volume  of  the  solution 
does  not  much  exceed  75  cc.  Avoid  boiling  to  very  small  bulk, 
as  in  that  case  some  of  the  precipitated  copper  may  redissolve. 
The  aluminum  should  now  appear  clean,  the  precipitated  copper 
being  detached  or  only  loosely  adhering.  Remove  from  the 
heat  and  wash  down  the  cover  and  sides  of  the  beaker  with 
hvdrogen  sulphide  water.  This  will  prevent  any  of  the  finely 
divided  copper  from  becoming  oxidized  and  dissolved  and  will 
also  precipitate  any  traces  of  copper  that  may  still  remain  in 
solution.  (It  should  be  understood  that  there  is  no  difficulty 
in  precipitating  all  the  copper  in  every  case.)  If  the  hydrogen 
sulphide  shows  there  was  more  than  a  very  little  copper  still 
in  solution  it  is  best  to  continue  the  boiling  for  a  short  time, 
diluting  the  liquid  to  about  75  cc.  if  necessary.  This  will 
coagulate  the  sulphide  and  render  it  easier  to  filter.  Finally, 
decant  through  a  g-cm.  filter  and  then,  without  delay,  transfer 
the  precipitate  to  the  filter  with  the  aid  of  a  jet  of  hydrogen 
sulphide  water,  leaving  the  aluminum,  as  clean  as  possible,  in 
the  beaker.  Wash  filter  and  precipitate  six  times  with  hydrogen 
sulphide  water,  allowing  to  drain  completely  each  time,  but  never 
permitting  the  filter  to  remain  thus  drained  until  finished,  or  the 
copper  may  oxidize  and  run  through.  Now  place  the  original 
clean  flask  under  the  funnel  and  then  open  the  filter  carefully 
and  spread  it  smoothly  in  the  funnel.  With  a  jet  of  hot  water, 
using  as  little  as  possible,  wash  the  precipitate  into  the  flask. 
Allow  5  cc.  of  strong  nitric  acid  to  run  from  a  small  pipette  over 
the  aluminum  in  the  beaker,  and  then  pour  from  the  beaker 
over  the  filter  to  dissolve  any  remaining  copper.  Without  wash- 
ing beaker  or  filter  at  this  stage,  collect  the  filter  into  small  com- 
pass with  a  glass  rod  and  push  it  gently  into  the  throat  of  the 


88  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

funnel.  Now  remove  the  flask  and  replace  it  with  the  beaker. 
Boil  the  mixture  in  the  flask  to  dissolve  the  copper  and  expel 
the  red  fumes,  and  then  again  place  the  flask  under  the  funnel. 
Now  pour  over  the  filter  5  cc.  or  more  of  saturated  bromine  water, 
enough  to  impart  a  distinct  color  to  the  liquid  in  the  flask. 
The  bromine  cleanses  any  residue  still  adhering  to  the  filter,  but 
its  most  important  function  is  to  insure  the  highest  state  of  oxida- 
tion of  any  arsenic  or  antimony  in  the  solution.  Next,  wash  the 
beaker  and  aluminum,  pouring  through  the  filter,  and  then  wash 
the  filter  six  times  with  hot  water.  If  the  operations  are  properly 
conducted,  the  final  volume  of  the  liquid  in  the  flask  need  not 
much  exceed  40  cc.  Boil  the  solution  until  the  excess  of  bromine 
is  entirely  expelled  and  the  volume  is  reduced  to  perhaps  25  cc. 
(A  boiling  rod  (i,  14)  will  entirely  prevent  bumping.)  Now 
add  a  slight  excess  of  ammonia  (usually  10  cc.  of  strong  ammonia), 
boil  off  most  of  the  excess,  add  acetic  acid  in  excess,  boil  a  minute, 
cool,  dilute  to  about  30  cc.  if  necessary,  add  potassium  iodide  (see 
5),  and  titrate  as  in  the  standardization  of  the  thiosulphate,  calcu- 
lating the  percentage  of  copper  accordingly. 

4.  It  is  best  to  boil  off  as  much  of  the  free  ammonia  as  possible, 
before  acidifying  with  acetic  acid,  in  order  to  avoid  the  formation 
of  too  much  ammonium  acetate,  which  has  a  retarding  effect 
on  the  reactions  of  the  subsequent  titration.  The  point  cannot 
be  told,  if  much  copper  is  present,  by  the  absence  of  an  ammoniacal 
odor,  as  the  blue  copper-ammonium  salt  gradually  decomposes 
and  gives  off  ammonia.  It  is  usually  best  to  add  the  acid  when  the 
smell  of  ammonia  has  become  rather  faint.  Boiling  too  long 
does  no  harm  unless  a  bluish  deposit  forms  on  the  flask.  This 
may  be  copper  arsenate  or  hydroxide",  which  frequently  dissolves 
with  great  difficulty  in  acetic  acid.  Always  look  for  this  deposit 
before  adding  the  acetic  acid,  and,  when  observed,  cautiously 
add  enough  ammonia  to  dissolve,  it,  again  boiling  off  any  great 
excess.  A  precipitate  of  any  nature,  due  to  overboiling,  which 


COPPER.  89 

does  not  deposit  on  the  flask,  will  usually  do  no  harm,  and  the 
copper  contents  will  be  subquently  taken  up  by  the  acid.  A 
light-colored  flocculent  precipitate,  sometimes  observed  in  the 
acetic  acid  solution,  perhaps  aluminum  hydroxide,  is  ordinarily 
without  effect.  If  the  cooling,  before  titration,  causes  the  separa- 
tion of  crystals  of  copper  acetate,  they  should  be  redissolved  by 
warming  with  a  little  more  water  and  the  solution  again  cooled. 

5.  Notes. — According    to    the    equation    previously   given, 
0.5  gram  of  copper  requires  2.61   grams  of  potassium  iodide. 
While  direct  experiment  shows  this  to  be  apparently  true,  yet 
when  only  the  theoretical  amount  of  potassium  iodide  is  present 
the  reaction  is  slow,  and  in  fact  does  not  appear  to  proceed  to 
completion  until  during  the  titration,  which  is  thereby  unduly 
prolonged.     It  is  best,  therefore,  to  always  use  an  excess,  but  as 
the  iodide  is  expensive  the  quantity  used  should  be  governed 
by  the  amount  of  copper  present,  which  can  always  be  estimated 
approximately.     Allow,  say,  i  gram  of  potassium  iodide  for  every 
15  per  cent,  copper,  when  0.5  gram  of  ore  is  taken  for  assay. 
It  is  convenient  to  prepare  a  solution  containing  50  grams  of 
potassium  iodide  in  100  cc.     A  2-cc.  pipette  will  thus  deliver 
i  gram  of  the  salt.     No  error  will  be  introduced  in  a  doubtful 
case  by  adding  more  potassium  iodide  after  the  titration  is  appar- 
ently finished  and  resuming  the  operation  if  the  blue  color  is 
thereby  restored. 

6.  Zinc  and  silver  do  not  interfere  with  the  assay.     Lead 
and  bismuth  are  without  effect,  except  that  by  forming  colored 
iodides  they  may  mask  the  approach  of  the  end-point  before 
adding    starch.     Arsenic    and    antimony,    under    the    treatment 
described,  have  no  influence.     The  return  of  the  blue  tinge  in 
the  titrated  liquid  after  long  standing  is  of  no  significance,  but  a 
quick  return,  which  an  additional  drop  or  two  of  the  thiosulphate 
does  not  permanently  destroy,  is  usually  an  evidence  of  faulty 
work. 


90  TECHNICAL   METHODS  OF   ORE  ANALYSIS. 

7.  In  such  as  case,  or  where  the  end-point  has  been  accidentally 
passed,  it  is  not  necessary  to  begin  the  assay  anew.     The  follow- 
ing procedure  will  enable  the  titration  to  be  repeated:  *  Add  10  cc. 
of  strong  nitric  acid  and  heat  the  mixture  to  boiling.     Heat  very 
cautiously  at  first  until  the  iodine  set  free  is  mostly  expelled, 
otherwise   the  mixture  may  foam   over.     Now  manipulate   the 
flask  in  a  holder  over  a  free  flame  and  boil  the  solution  down  as 
rapidly  as  desired  until  only  about  5  cc.  are  left.     Dilute  with 
25  cc.  of  hot  water  and  boil  again  for  a  short  time  to  expel  any 
red  fumes.     Now  add  a  slight  excess  of  ammonia  and  finish  in 
the  usual  way. 

8.  Rapid    Assay  by   the    Iodide    Method.  —  The    following 
scheme   has    frequently   proved  useful  where  extreme  accuracy 
was     not    necessary.      As     a     rule     the    results    are    a    trifle 
low,  but  the   error  does  not  usually  exceed  0.10-0.15  °f  J  Per 
cent. 

Treat  0.5  gram  of  the  ore  in  an  8-oz.  Erlenmeyer  flask  with 
10  cc.  of  strong  nitric  acid.  Heat  gently  until  the  decomposi- 
tion of  the  copper  compounds  is  complete,  then  add  5  cc.  more 
of  nitric  acid  and  5  grams  of  potassium  chlorate.  Continue  the 
heating,  either  on  a  hot  plate  or  with  a  thin  asbestos  sheet  under 
the  flask  (i,  13),  just  to  complete  dryness,  avoiding  overheating 
and  baking.  Allow  to  cool,  add  25  cc.  of  strong  ammonia  and 
10  cc.  of  water.  Heat  gently  to  effect  thorough  disintegration  of 
the  residue  and  solution  of  the  copper  and  then  filter  through  a 
9-cm.  filter,  washing  with  cold  water.  Receive  the  filtrate  in  an 
8-oz.  flask.  Boil  until  the  excess  of  ammonia  is  expelled  and  the 
liquid  reduced  to  perhaps  25  cc.,  then  acidify  with  acetic  acid, 
boil  a  minute  and  finish  in  the  usual  manner. 

*  Another,  and  easier,  method  is  to  add,  from  a  burette,  a  counted  number 
of  drops  of  permanganate  solution,  of  any  strength,  until  the  color  returns. 
Titrate,  repeat  the  same  addition  of  permanganate,  again  titrate  and  deduct. 


COPPER.  gi 

9.  Electrolytic   Method. — To  i   gram  of  the  ore  in  an  8-oz 
flask  add  10  cc.  of  strong  hydrochloric  acid  and  5  cc.  of  strong 
nitric  acid.     Boil  gently  until  decomposition  is  complete,  using 
more  of  the  acids  if  necessary.     If  the  evaporation  of  the  liquid 
causes  a  separation  of  soluble  salts,  add  enough  hydrochloric 
acid  at  the  end  to  again  bring  them  into  solution.     Finally,  add 
7  cc.  of  strong  sulphuric  acid  and  boil,  best  over  a  free  flame, 
to  abundant  fumes.     After  cooling,  boil  with  about  30  cc.  of  water 
for  a  moment  and  then  allow  to  stand,  hot,  until  any  anhydrous 
ferric  sulphate  has  entirely  dissolved.     If  silver  is  liable  to  be 
present  add  a  single  large  drop  of  strong  hydrochloric  acid  just 
previous   to   the   boiling,   to   precipitate  it  as   chloride.     Filter, 
washing  filter  and  residue  at  least  six  times  with  hot  water.     Dilute 
the  filtrate  to  about  300  cc.   (the  dilution  is  unnecessary  if  the 
amount  of  copper  is  small)  and  pass  in  hydrogen  sulphide  until 
the  copper  is  all  precipitated,  as  shown  by  the  clear  condition 
of  the  supernatant  liquid.     Filter  off  the  sulphides,  washing  well 
with  hydrogen  sulphide  water.     Now  rinse  the  precipitate  back 
into  the  beaker  as  completely  as  possible  with  hot  water,  place  the 
beaker   under   the   funnel   and  pour   through   the  latter  a  hot 
mixture   of   5  cc.   of  a  moderately  strong  colorless  solution  of 
sodium   sulphide    (see  p.  29)  and  15  cc.  of  water.     Remove  the 
beaker,  stir  the  contents  well,  and,  either  immediately  or  after 
warming  a  few  minutes,  according  to  the  amount  of  arsenic  and 
antimony  apparently  present,  filter  through  the  last  filter  again. 
A  second  extraction  is  rarely  necessary.     Wash  out  the  beaker 
with  hot  water  and  then  wash  the  precipitate  well  with  hot  dilute 
sodium   sulphide   solution.     Reserve   the   filtrate,   which  almost 
invariably  contains  a  little  dissolved  copper.     Rinse  the  residue 
back  into  the  beaker  with  hot  water,  using  as  little  as  possible. 
It  is  difficult  to  get  the  filter  very  clean  and  it  is  not  necessary. 
Place  beaker  and  contents  once  more  under  the  funnel  and  pour 


92  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

through  the  latter  a  hot  solution  of  about  2  grams  of  potassium 
cyanide  in  about  15  cc.  of  water.  Remove  the  beaker  and 
replace  it  with  the  original  flask.  Heat  and  stir  the  mixture  in 
the  beaker  until  the  copper  sulphide  is  all  dissolved,  adding 
more  potassium  cyanide  if  required,  but  avoiding  a  great  excess. 
Sulphides  of  bismuth,  cadmium,  etc.,  will  remain  undissolved. 
Again  filter  through  the  last  filter  and  wash  ten  times  with  hot 
water.  Use  small  washes  each  time  to  avoid  a  bulky  filtrate. 
Remove  flask  and  filtrate  to  a  hood,  add  5-6  cc.  of  strong  sul- 
phuric acid  (this  is  usually  a  sufficient  excess),  heat  to  boiling 
and  boil  to  fumes.  Finally,  finish  over  a  free  flame  until  nearly 
all  the  excess  of  acid  is  expelled.  Allow  to  cool  with  the  flask 
inclinrd,  to  prevent  the  cake  which  may  form  from  cracking 
th3  glass.  The  addition  of  a  little  nitric  acid  to  the  sulphuric 
acid  mixtu-e  causes  a  more  rapid  solution  of  the  copper  sulphide, 
but  this  is  a  disadvantage  as  the  mixture  is  then  liable  to  bump 
badly.  Dissolve  the  cool  cake  or  residue  in  about  25  cc.  of  water. 
During  these  operations  attention  may  be  turned  to  the  reserved 
filtrate,  which  usually  contains  an  appreciable  amount  of  copper. 
Acidify  it  with  hydrochloric  acid,  s'.ir  well  to  coagulate  the  pre- 
cipitated sulphur,  filter,  and  wash  with  hydrogen  sulphide  water. 
Ignite  the  filter  and  contents  in  a  platinum  dish  at  a  dull  red 
heat  until  the  carbon  of  the  paper  is  entirely  consumed.  Be 
very  careful  to  do  this  at  as  low  a  temperature  as  possible.  All 
the  arsenic  and  antimony  will  be  expelled.  Warm  the  residue 
with  a  few  drops  of  nitric  acid  and  add  the  solution  to  the  main 
porlion  in  the  flask.  To  the  latter  now  add  3  cc.  of  strong  nitric 
acid,  transfer  the  solution  to  a  suitable  beaker,  dilute,  and 
electrolyze  as  described  below. 

10.  Electrolysis  of  the  Copper  Solution. — The  solution  should 
have  a  volume  of  about  125  cc.  and  contain  several  cubic  centi- 
meters of  strong  nitric  acid  (sp.  gr.  1.42).  The  amount  of  free 


C  OFFER.  93 

nitric  acid  necessary  is  not  narrowly  limited.  It  is  gradually 
changed  to  ammonia  by  the  electrolysis,  and  therefore,  if  too  little 
be  present,  the  solution  may  become  alkaline.  On  the  other 
hand,  too  much  acid  retards  or  may  prevent  the  deposition  of 
the  copper.  I  usually  use  an  excess  of  about  3  cc.  in  the  above 
volume  of  liquid,  but  7  or  8  cc.  may  be  safely  employed,  with  the 
advantage  of  preventing  in  a  large  measure  the  deposition  of 
any  arsenic  that  may  have  escaped  extraction. 

The  following  apparatus  may  be  used:  A  cathode  consisting 
of  a  plain  platinum  cylinder  5  cm.  long  and  2.5  cm.  in  diameter. 
It  has  a  total  surface  of  about  78.5  sq.  cm.  and  weighs  about 
12.5  grams.  .It  is  supported  by  a  strong  platinum  wire  attached 
to  the  top.  An  anode  consisting  of  a  stout  platinum  wire 
rising  from  the  center  of  a  base  made  by  coiling  the  wire  around 
itself  closely  so  as  to  form  a  circular  disc.  It  weighs  about  8.5 
grams.  A  beaker  suitable  for  the  above  electrodes,  having  a 
diameter  of  about  5  cm.  and  a  height  of  about  8-9  cm. 

The  volume  and  acidity  of  the  solution  having  been  properly 
adjusted  and  the  cathode  cleaned,  ignited,  and  weighed,  the 
electrodes  are  inserted  and  suitably  supported  in  the  beaker 
and  the  latter  is  covered  with,  a  split  watch-glass,  which  permits 
the  wires  to  pass  through  the  center,  leaving  an  opening  of  only 
a  small  crack.  Adjust  the  anode  within  the  cathode  with  its 
base  almost  touching  the  bottom  of  the  beaker.  The  bottom 
of  the  cathode  should  come  about  one-fourth  of  an  inch  above 
the  base  of  the  anode,  and  the  top  of  the  cylinder  should  project 
a  little  above  the  surface  of  the  solution. 

Now  connect  with  the  battery  and  electrolyze.  The  cathode 
should  be  connected  with  the  zinc  pole  of  the  battery.  The 
current  density  should  be  NDioo  =  0.5-1  amp.  Electrode  tension, 
2.2-2.5  vo^ts.  Temperature,  2o°-3o°  C.  Time  required,  4  to  5 
hours.  For  details  as  to  the  attainment  of  these  conditions  see 


94  TECHNICAL    METHODS  OF  ORE  ANALYSIS. 

article  ELECTROLYSIS,  p.  10.  (In  my  own  work,  using  a  direct 
2  20- volt  current  from  a  dynamo  and  a  bank  of  lamps  as  a  resist- 
ance— which  reduces  the  tension  to  about  2.2  volts — I  usually 
employ,  with  the  above  apparatus,  from  0.2  to  0.4  amp.,  accord- 
ing to  the  amount  of  copper  present,  and  allow  to  run  over  night.) 

When  the  solution  has  become  colorless  and  the  copper  is 
apparently  all  deposited,  immerse  the  cathode  deeper  in  the 
liquid,  or  better,  raise  the  level*  of  the  latter  by  rinsing  the  cover 
and  sides  of  the  beaker,  and  allow  the  current  to  run  for  half 
an  hour  longer.  The  fresh  platinum  surface  will  show  whether 
copper  still  remains  in  solution.  Finally,  at  the  end,  lower  the 
beaker  from  the  electrodes,  with  the  current  still  passing,  and 
at  the  same  time  rinse  off  the  adhering  acid  solution  with  a 
stream  from  the  wash-bottle.  Immediately  replace  the  beaker 
with  another  of  distilled  water  and  then  stop  the  current.  Re- 
move the  cathode  and  wash  off  the  water  with  alcohol.  Allow  to 
drain  a  moment  on  filter-paper  and  then  dry  at  about  100°  C, 
cool  to  room  temperature,  and  weigh.  The  excess  over  the 
original  weight  of  the  electrode  represents  the  copper  in  the 
weight  of  ore  taken. 

It  is  always  a  good  plan  to  clean  the  electrode  again  with 
nitric  acid,  and  after  igniting  and  weighing  it,  replace  it  once 
more  in  the  solution  and  electrolyze  for  a  short  time  to  make 
certain  that  all  the  copper  is  removed. 

The  above  description  will  serve  very  well  for  those  who 
have  to  make  electrolytic  copper  assays  only  occasionally.  By 
means  of  special  arrangements  of  a  less  simple  nature,  including 
the  rapid  rotation  of  one  of  the  electrodes,  all  the  copper  in  an 
assay  can  be  satisfactorily  deposited  very  quickly,  perhaps  in 
15  minutes.  Detailed  descriptions  of  experiments  in  this  direc- 
tion can  be  found  in  the  chemical  literature  of  the  past  few  years. 
(See  foot-note,  p.  15.) 


COPPER.  95 

ii.  Electrolytic  Methods  of  the  Anaconda  Copper  Mining 
Co.* — Allow  about  o.n  ampere  for  each  determination.  With 
the  present  arrangements  at  Anaconda  this  gives  a  tension  of 
from  1.40  to  2.30  volts. 

In  all  cases  a  drop  of  the  electrolyte  is  brought  in  contact 
with  a  drop  of  hydrogen  sulphide  water  to  test  if  copper  has 
been  completely  deposited. 

The  platinum  cylinders  with  deposited  copper  are  washed  in 
water,  then  alcohol,  dried  on  a  steam-bath,  and  weighed. 

If  the  deposited  copper  is  dark  from  presence  of  arsenic,  it  is 
dissolved  in  8  cc.  of  nitric  acid,  diluted  with  water  and  elec- 
trolyzed  again,  care  being  taken  to  remove  from  the  current  soon 
after  the  complete  deposition  of  the  copper. 

Copper  may  be  separated  from  bismuth,  antimony,  and 
arsenic  by  precipitation  as  sulphocyanate.  The  precipitate  is 
washed  thoroughly,  ignited  gently  in  a  porcelain  crucible,  dis- 
solved in  7  cc.  of  nitric  acid,  and  the  copper  is  then  determined 
electrolytically. 

In  samples  containing  arsenic,  antimony,  tellurium,  and 
selenium,  such  as  electrolytic  slimes,  add  100  mgs.  of  iron  to  the 
nitric  acid  solution  of  the  sample  from  which  silver  has  been 
removed  as  chloride.  Add  ammonia  to  precipitate  irgn  and 
still  have  the  solution  acid.  Bring  to  a  boil,  settle,  filter  off 
the  iron  precipitate,  redissolve  it,  and  again  precipitate  as 
before.  A  third  precipitation  may  be  necessary  to  be  certain 
of  having  all  the  copper  in  solution.  Combine  the  filtrates, 
evaporate  sufficiently,  add  nitric  acid,  and  electrolyze.  The 
iron  precipitate  holds  the  arsenic,  antimony,  tellurium,  and 
selenium. 

Converter  Copper. — Dissolve  0.5  gram  in  8  cc.  nitric  acid, 
8  cc.  water  and  i  cc.  sulphuric  acid,  keeping  the  beaker  covered 

*  F.  W.  Traphagen,  Western  Chem.  and  Met.,  Vol.  6,  192. 


96  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

during  solution.  When  solution  is  complete  and  the  fumes 
expelled,  dilute  with  water  and  electrolyze. 

In  the  copper  determinations  on  mattes  and  converter  copper, 
the  percentage  of  silver,  as  determined  by  fire  assay,  is  deducted 
from  the  combined  percentages  of  copper  and  silver  found  by 
electrolysis.  (291.66  oz.  =  i  per  cent.)  The  silver  may  be  pre- 
cipitated with  just  sufficient  dilute  sodium  chloride  solution, 
taking  care  to  avoid  an  excess,  and  after  filtering  off  the  silver 
chloride,  the  copper  deposited  alone. 

Mattes. — Moisten  i  gram  of  the  sample  with  a  few  drops  of 
water,  add  8  cc.  of  nitric  acid  and  i  cc.  of  sulphuric  acid.  Run 
to  dryness  on  steam-bath.  Take  up  with  water  and  8  cc.  of 
nitric  acid.  Filter  and  electrolyze. 

Slags. — Decompose  2  grams  in  a  platinum  dish  with  8  cc. 
nitric  acid,  8  cc.  hydrofluoric  acid,  and  i  to  2  cc.  sulphuric  acid. 
Evaporate  to  sulphuric  acid  fumes.  Take  up  with  water  and 
10  cc.  of  nitric  acid  and  electrolyze. 

Sulphide  Ores. — Weigh  i  gram  of  the  sample  into  a  beaker 
(3^  inches  high  and  2\  inches  in  diameter).  Add  8  cc.  of  nitric 
acid  and  a  little  potassium  chlorate.  Evaporate  to  complete 
dryness  on  steam  bath.  Take  up  with  water  and  from  6  to  10  cc. 
of  nitric  acid.  Dilute  sufficiently,  allow  to  settle  and  then  elec- 
trolyze. 

Oxidized  Ores. — Take  i  gram  of  the  sample.  Evaporate  to 
dryness  with  8  cc.  of  nitric  acid.  Add  10  cc.  of  hydrochloric 
acid  and  2  cc.  of  sulphuric  acid,  and  evaporate  to  sulphuric  acid 
fumes.  Take  up  with  water  and  8  cc.  of  nitric  acid,  dilute  suffi- 
ciently, settle,  and  electrolyze. 

12.  Rapid  Electrolytic  Method. — By  employing  a  strong  cur- 
rent copper  can  be  deposited  very  rapidly,  but,  in  the  ordinary 
electrolytic  cell,  much  of  the  deposit  is  then  apt  to  be  non-coherent 
or  detached  and  quite  unfit  for  handling  and  weighing.  This 


COPPER. 


97 


trouble  has  been  overcome  by  the  use  of  arrangements  which 
rotate  one  of  the  electrodes  or  the  electrolyte.  These  devices  are 
complicated  and  costly.  Quite  recently  it  has  been  found  that 
almost  equal  rapidity  may  be  attained  by  the  use  of  a  specially 
prepared,  gauze  cathode.*  This  electrode  is  made  of  52-mesh 
platinum  wire  gauze.  It  is  about  i  inch  in  diameter  and  i^ 
inches  long,  of  cylindrical  shape  and  corrugated  and  sand-blasted. 
With  75  cc.  of  solution  and  a  current  of  from  8  to  10  amperes 
and  3  to  4  volts,  the  copper  is  usually  completely  deposited  in 
from  10  to  15  minutes.  The  character  of  the  deposit  on  the  pre- 
pared electrode  is  all  that  could  be  desired. 

Ores  may  be  treated  as  described  in  9  until  the  copper,  free 
from  interfering  elements,  is  finally  obtained  in  solution  as  sul*- 
phate.  Neutralize  the  excess  of  sulphuric  acid  with  ammonia, 
then  add  an  excess  of  3  cc.  of  strong  nitric  acid,  transfer  to  a 
tall  electrolysis  beaker,  dilute  to  75  cc.  and  electrolyze  with  a  cur- 
rent of  the  above  strength.  The  end  of  the  operation  may  be 
determined  by  testing  a  drop  of  the  electrolyte  with  a  drop  of 
hydrogen  sulphide  water. 

In  the  absence  of  interfering  elements  the  process  may  be 
greatly  simplified,  even  omitting  filtration  when  the  insoluble  res- 
idue is  slight  or  settles  well.  The  final  conditions,  however,  as 
described  above,  must  always  be  the  same,  and  the  solution  must 
be  free  from  chlorides. 

Arsenic,  if  present  only  in  small  amount,  will  not  deposit  with 
the  copper.  Therefore,  if  the  deposited  copper  is  darkened  with 
arsenic,  it  usually  suffices  to  redissolve  it  in  nitric  acid  and  deposit 
it  once  more. 

13.  Cyanide  Method. — In  this  method  the  copper  is  obtained 
in  a  blue  ammoniac  al  solution  and  its  amount  is  estimated  from 

*  R.  C.  Benner,  Jour.  Ind.  and  Eng.  Chem.,  May,  1910.  Banner's  electrodes 
may  be  obtained  of  the  Denver  Fire-Clay  Co. 


gS  TECHNICAL  METHODS    OF   ORE  ANALYSIS. 

the  quantity  of  standard  solution  of  potassium  cyanide  required 
to  discharge  the  blue  color.  The  results  of  the  cyanide  titration 
are  exact  if  certain  conditions  are  always  maintained.  It  is 
found  that  for  the  same  amount  of  copper: 

1.  A  concentrated  solution  requires  more  cyanide  for  decolora- 
tion than  a  dilute  solution. 

2.  A  hot  solution  requires  less  cyanide  than  a  cold  one. 

3.  In  any  case  when,  from  a  rapid  addition  of  cyanide,  the 
color  has  become  rather  faint,  it  may,  by  simple  standing,  con- 
tinue to  fade,  and  perhaps  entirely  disappear. 

4.  If  the  amount  of  cyanide  added  is  insufficient  to  effect 
complete  discharge  of  color,  even  after  allowing  the  copper  solu- 
tion to  stand  for  several  minutes,  the  titration  may  then  be  finished 
without  alteration  of  the  final  result. 

From  the  foregoing  facts  it  is  evidently  necessary,  in  order 
to  obtain  correct  results,  that  the  titrations  for  unknown  amounts 
of  copper  should  be  made  under  conditions  that  do  not  differ 
materially  in  the  following  particulars  from  those  governing 
the  standardization  of  the  cyanide  solution: 

1.  Temperature. 

2.  Rapidity  of  the  final  additions  of  cyanide. 

3.  Final  volume  of  solution. 

Besides  the  physical  conditions  just  enumerated,  there  are 
chemical  conditions  that  effect  the  result,  such  as  presence  of  a 
large  amount  of  chlorides,  a  large  excess  of  ammonia,  etc.  Such 
abnormal  conditions  require  no  special  consideration,  since 
they  are  all  easily  avoided  by  following  the  method  to  be 
describ:d. 

14.  Standardization  of  the  Cyanide  Solution. — Dissolve  pure 
potassium  cyanide  in  distilled  water  in  the  proportion  of  2 1  grams 
to  the  liter.  Weigh  accurately  about  0.2  gram  of  pure  copper  foil 
and  dissolve  it  in  an  8-oz.  flask  in  5  cc.  of  strong  nitric  acid  (sp.  gr. 


COPPER.  99 

1.42).  Dilute  with  25  cc.  of  water  and  add  5  cc.  of  a  saturated  solu- 
tion of  bromine  in  cold  water.  Boil  the  mixture  until  the  bromine 
i~  apparently  expelled.  Now  add  50  cc.  of  cold  water  and  10  cc. 
of  strong  ammonia  (sp.  gr.  0.90).  Cool  to  the  ordinary  tempera- 
ture by  placing  under  a  tap  or  in  cold  water.  Titrate  with  the 
cyanide  solution  in  a  slow,  cautious  manner,  and  as  the  end-point 
is  approached,  as  shown  by  the  partial  fading  of  the  blue  color, 
add  distilled  water  so  as  to  bring  the  volume  of  the  solution  to 
approximately  150  cc.  Finish  the  titration  by  careful  and  regu- 
lar additions  of  cyanide,  finally  decreasing  to  a  drop  at  a  time 
and  agitating  the  flask  with  a  rotary  movement  after  each  addi- 
tion, until  the  blue  tint  can  no  longer  be  detected  by  holding  the 
flask  against  a  light-colored  background.*  It  is,  of  course,  very 
essential  that  there  should  be  no  haste  and  no  prolonged  delay 
in  these  final  additions  of  cyanide.  Simply  adopt  a  regular, 
natural  manner,  that  can  easily  be  repeated  in  all  subsequent 
titrations. 

From  the  amount  of  cyanide  solution  required  for  the  weight 
of  copper  taken,  calculate  the  value  of  i  cc.  in  copper. 

Keep  the  standard  solution  in  a  cool  place  not  exposed  to 
direct  sunlight.  Under  these  circumstances  it  holds  its  strength 
fairly  well,  but  still  it  gets  weaker  from  the  decomposition  of  the 
cyanide  and  should  be  restandardized  weekly. 

15.  Treatment  of  Ores,  etc. — Treat  i  gram,  or  0.5  gram  if 
the  material  seems  to  contain  40  per  cent,  or  over,  in  an  8-oz. 
flask  with  10  cc.  of  strong  nitric  acid.  Boil  gently  until  decom- 
position appears  to  be  complete  and  then  add  about  7  cc.  of 
s  rong  sulphuric  acid  and  heat  ihe  mixture  over  a  free  flame  until 
all  the  nitric  acid  is  expelled  and  the  residuary  sulphuric  acid  is 
boiling  freely  and  evolving  copious  fumes.  Remove  from  the 

*  Some  operators  prefer  a  porcelain  casserole  and  stirring-rod  to  a  flask. 


100  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

flame  and  allow  to  cool.  Ores  that  are  not  decomposed  by  this 
treatment  must  be  attacked  in  some  special  manner  for  which  no 
general  directions  can  be  given.  Sometimes  the  addition  of 
hydrochloric  acid  is  all  that  is  necessary.  It  is  advisable  in  any 
case  not  to  add  the  sulphuric  acid  until  the  ore  appears  to  be  well 
decomposed. 

To  the  residue  in  the  flask  add  20  cc.  of  cold  water  and  heat 
the  mixture  to  boiling.  If  the  ore  is  liable  to  contain  an  appre- 
ciable amount  of  silver,  add  a  single  drop  of  strong  hydrochloric 
acid  and  agitate  the  liquid  so  as  to  collect  the  silver  chloride  in 
clots.  One  percent. of  silver,  or  292  ozs.  per  ton  of  2000  Ibs.,  will 
increase  the  apparent  copper  contents  about  0.29  per  cent.  Allow 
to  stand,  hot,  until  any  anhydrous  ferric  sulphate  is  entirely 
dissolved  and  then  filter,  washing  flask  and  filter  with  hot  water. 
Return  the  filtrate  to  the  original  flask.  The  volume  of  the 
solution  should  not  much  exceed  60  cc.  at  this  point.  Now  place 
in  the  flask  3  pieces  of  stout  sheet  aluminum,  each  about  ij 
inches  long  by  f  inch  wide,  and  heat  the  mixture  to  boiling. 
Boil  for  perhaps  5  or  10  minutes,  according  to  the  volume  of  the 
liquid  and  the  appearance  of  the  aluminum.  When  the  copper 
is  all  precipitated  the  aluminum  will  usually  appear  bright  and 
clean,  or  it  will  become  clean  by  agitating  the  flask  so  as  to  loosen 
the  adhering  copper.  Remove  from  the  lamp>  add  about  15  cc. 
of  strong  hydrogen  sulphide  water,  which  will  insure  the  com- 
plete precipitation  of  the  copper,  allow  to  settle  a  moment,  and 
then  decant  through  a  9-cm.  filter,  retaining  in  the  flask  the  alu- 
minum and  as  much  of  the  copper  as  possible.  Wash  the  pre- 
cipitated copper  2  or  3  times  by  decantation  with  weak  hydrogen 
sulphide  water,  using  about  25  cc.  each  time  and  pouring  through 
the  filter.  Drain  the  flask  as  completely  as  possible  the  last 
time.  Now  place  the  flask  under  the  funnel  and  pour  through 
the  latter  10  cc.  of  a  warm  mixture  of  equal  volumes  of  strong 


COPPER.  I0i 

nitric  acid  and  water.  Do  not  wash  the  filter  at  this  point,  but 
remove  the  flask  and  replace  it  with  a  beaker.  Shake  the  acid 
about  in  the  flask  gently,  so  as  to  dissolve  all  the  copper,  warming 
slightly  if  necessary,  but  avoid  heating  more  than  is  required  to 
just  dissolve  the  copper,  or  the  aluminum  may  be  attacked  When 
solution  is  complete,  pour  the  entire  contents  of  the  flask  into  the 
beaker  that  was  placed  under  the  funnel,  washing  only  the  lip 
of  the  flask,  and  then  pour  the  solution  back  into  the  flask  again, 
retaining  the  aluminum  in  the  beaker.  Wash  the  aluminum 
thoroughly  and  then  replace  the  flask  under  the  funnel.  Now 
pour  into  the  filter  5  cc.  of  a  cold  saturated  solution  of  bromine 
in  water,  and  when  it  has  run  through  wash  the  filter  with  hot 
water.  The  bromine  is  to  cleanse  any  dark  sulphur  left  from 
the  copper  sulphide  on  the  filter.  In  the  above  operations 
avoid  increasing  the  bulk  of  the  solution  more  than  necessary. 
Boil  the  solution  in  the  flask  until  the  bromine  is  expelled,  then 
cool  somewhat  and  add  10  cc.  of  strong  ammonia  (sp.  gr.  0.90) 
and  then  continue  the  cooling  to  room  temperature.  Titrate 
the  cool  solution  with  the  standard  cyanide  solution  cautiously 
until  the  blue  color  is  discharged  to  a  considerable  extent  and 
it  is  evident  that  the  end-point  is  not  far  off. 

The  liquid  is  now  frequently  more  or  less  cloudy.  When 
this  is  the  case  it  should,  for  accurate  work,  be  filtered.  If  the 
titration  has  been  carried  too  far  before  filtration,  the  faint-blue 
tinge  is  liable  to  fade  completely  away,  thus  spoiling  the  assay. 
On  the  other  hand,  if  filtered  early  in  the  titration,  a  second  milki- 
ness  may  develop  later.  Filter  the  partially  titrated  solution 
through  a  12.5-011.  filter.  One  washing  will  usually  suffice. 
Finish  the  titration  very  carefully  on  the  clear,  pale-blue  solution, 
precisely  as  in  the  standardization  previously  described.  Toward 
the  end  dilute  if  necessary,  so  as  to  obtain  a  final  volume  of  about 
150  cc. 


102  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

The  number  of  cubic  centimeters  of  cyanide  solution  required, 
multiplied  by  the  copper  value  of  i  cc.,  will  give  the  weight  of 
copper  contained  in  the  amount  of  ore  taken,  from  which  the 
percentage  is  readily  calculated. 

None  of  the  ordinary  constituents  of  ores  interfere  with  the 
method  as  described. 

16.  Permanganate  Method.*  —  In  this  method  the  copper 
is  precipitated  as  cuprous  thiocyanate.  This  is  subsequently 
decomposed  with  sodium  hydroxide  with  the  formation  of  sodium 
thiocyanate,  and  the  solution  of  the  latter,  after  acidifying  with 
sulphuric  acid,  is  titrated  with  standard  potassium  permanganate 
solution.  The  decomposition  and  titration  are  in  accordance 
with  the  following  reactions  : 

CuCNS  +  NaOH  =  CuOH  +  NaCNS, 


6K2SO4  +  1  2MnSO4  +  loHCN  +  8H2O. 

The  permanganate  solution  is  made  of  such  a  strength  that 
i  cc.  =  10  mgm.  Fe.  Theoretically,  the  factor  for  copper  from 
the  iron  value  is  0.1897,  but,  owing  to  the  slight  solubility  of  the 
cuprous  thiocyanate,  the  actual  factor  for  small  percentages  of 
copper  under  the  above  conditions  is  0.200. 

17.  Treatment  for  Low-grade  Material.  —  Weigh  2  grams 
into  a  150-cc.  beaker,  add  8  cc.  of  strong  nitric  acid  and  evap- 
orate to  dryness.  In  most  cases  simple  dryness  is  sufficient, 
but  if  gelatinous  silica  is  present,  the  drying  should  be  more  com- 
plete. To  the  residue  add  2  cc.  of  hydrochloric  acid,  heat  to 
boiling,  add  20  cc.  of  hot  water  and  filter.  Heat  the  nitrate  and 
add  10  cc.  of  a  10  per  cent,  sodium  sulphite  solution,  and  when 
the  liquid  is  colorless  add  5  cc.  of  10  per  cent,  potassium  thio- 

*  G.  A.  Guess,  private  communication,  and  Jour.  Am.  Chem.  Soc.,  XXIV. 


COPPER.  103 

cyanate  solution  and  heat  to  boiling  to  coagulate  the  precipitate. 
Filter  through  a  double  n-cm.  filter  and  wash  thoroughly  with 
hot  water  to  remove  all  soluble  thiocyanates.  Now  place  a  clean 
beaker  or  flask  under  the  funnel  and  thoroughly  wash  the  filter 
and  precipitate  once  with  boiling  8  per  cent,  sodium  hydroxide 
solution,  contained  in  a  wash-bottle,  and  then  wash  thoroughly 
with  hot  water.  Finally,  make  the  alkaline  filtrate  decidedly  acid 
with  dilute  sulphuric  acid  and  titrate  to  the  usual  pink  tinge  with 
standard  potassium  permanganate. 

The  only  point  to  watch  carefully  is  the  acidity  at  the  time 
of  adding  the  sodium  sulphite  and  thiocyanate.  When  only  a 
few  milligrams  of  copper  are  present  the  amount  of  free  acid 
should  not  exceed  about  2  per  cent.,  as  otherwise  the  precipitation 
may  fail  to  take  place.  In  such  a  case  the  excess  of  acid  may  be 
neutralized  by  the  further  addition  of  sodium  sulphite  after 
adding  the  thiocyanate.  With  ordinary  care,  however,  the 
trouble  will  not  occur.  No  elements  interfere. 

18.  Treatment  for  Ores. — Weigh  '0.5  gram  of  the  ore  into  a 
300-cc.  beaker,  add  5  cc.  of  strong  nitric  acid,  heat  until  decom- 
position is  complete  and  then  evaporate  until  the  beaker  is  almost 
dry,  finally  adding,  while  the  beaker  is  still  over  the  heat,  3  cc. 
of  strong  hydrochloric  acid,  followed  by  75  cc.  of  hot  water. 
If  silver  is  present  in  appreciable  amount,  it  would  cause  an  error 
in  the  result  unless  removed  by  filtration  at  this  point,  but  if  absent 
or  negligible,  as  is  usually  the  case,  the  filtration  may  be  omitted. 
To  the  hot  solution,  or  filtrate,  add  5  cc.  of  a  loper  cent,  solution 
of  sodium  sulphite,  and  then,  after  decolorization  of  the  liquid, 
5  cc.  of  a  10  per  cent,  solution  of  potassium  thiocyanate.  Heat 
to  boiling  to  effect  coagulation  of  the  precipitate  and  then  filter 
and  wash  thoroughly  with  hot  water,  using  a  double  n-cm.  filter. 

Decompose  the  precipitate  with  sodium  hydroxide  solution 
and  finish  the  assay  as  described  in  17. 


104 


TECHNICAL  METHODS  OF    ORE  ANALYSIS. 


Cc. 

%  Cu. 

Cc. 

%  Cu. 

Cc. 

%  Cu. 

Cc. 

%  Cu. 

Cc. 

%  Cu. 

O.  I 

0.04 

5-i 

2.09 

10.  I 

4-13 

i5-i 

6.16 

20.  I 

8.18 

O.2 

0.08 

S-2 

2.  12 

IO.2 

4.17 

J5-2 

6.  20 

20  2 

8.22 

°-3 

O.  12 

5-3 

2.18 

I0.3 

4.21 

15-3 

6.24 

20-3 

8.26 

0.4 

o.  16 

5-4 

2.23 

IO-4 

4.25 

15-4 

6.28 

2O.4 

8.30 

°-5 

O.2O 

5-5 

2.27 

10.5 

4.29 

15-5 

6.32 

20.5 

8-34 

0.6 

O.24 

5-6 

2.3I 

10.6 

4-33 

15-6 

6.38 

20.  6 

8.38 

0.7 

0.28 

5-7 

2-35 

10.7 

4-37 

15-7 

6.42 

20.7 

8.42 

0.8 

0.32 

5-8 

2-39 

10.8 

4.41 

15.8 

6-45 

20.8 

8.46 

0.9 

o-37 

5-9 

2.42 

10.9 

4-45 

15-9 

6-49 

20.9 

8.50 

I.O 

0.41 

6.0 

2.46 

II.  O 

4-49 

16.0 

6-53 

21.0 

8-54 

.  i 

0-45 

6.1 

2.50 

ii.  i 

4-53 

16.1 

6.56 

21.  I 

8.58 

.2 

0.49 

6.2 

2-54 

II.  2 

4-55 

16.2 

6.60 

21.2 

8.62 

•3 

o-53 

6-3 

2.58 

M.-3 

4.62 

16.3 

6.64 

21.3 

8.66 

•4 

°-57 

6.4 

2-63 

11.4 

4.66 

16.4 

6.68 

21.4 

8.70 

•5 

0.61 

6-5 

2.67 

"••S 

4.70 

16.5 

6.72 

21-5 

8.74 

.6 

0.64 

6.6 

2.71 

ii.  6 

4-74 

16.6 

6.76 

21.6 

8.78 

•7 

•  0.68 

6.7 

2-75 

11.7 

4.78 

16.7 

6.80 

21.7 

8.82 

.8 

0.72 

6.8 

2-79 

ii.  8 

4.82 

16.8 

6.84 

21.8 

8.86 

•9 

0.77 

6.9 

2.83 

11.9 

4.86 

16.9 

6.88 

21.9 

8.90 

2.O 

0.82 

7.0 

2.87 

12.  O 

4.90 

17.0 

6-93 

22.0 

8.96 

2.  I 

0.86 

7-i 

2.91 

12.  I 

4-94 

17.1 

6-97 

22.1 

9.00 

2.2 

0.90 

7-2 

2-95 

12.2 

4-98 

17.2 

7.01 

22.  2 

9.04 

2-3 

o-93 

7-3 

2-99 

I2.3 

5.02 

17-3 

7-05 

22.3 

9.08 

2.4 

0.97 

7-4 

3-04 

12.4 

5.06 

17.4 

7.09 

22.4 

9.12 

2-5 

I.OO 

7-5 

3.08 

12.5 

5.10 

J7-5 

7-i3 

22.5 

9.  16 

2.6 

1.04 

7.6 

3-i3 

12.6 

5-14 

17.6 

7.17 

22.6 

9.20 

2-7 

1.  08 

7-7 

3-i7 

12.7 

5-i8 

17.7 

7.21 

22.7 

9.24 

2.8' 

1.14 

7.8 

3-20 

12.8 

5-22 

17.8 

7-25 

22.8 

9.28 

2-9 

1.18 

7-9 

3-24 

12.9 

5-26 

17.9 

7.29 

22.9 

9-32 

3-o 

1.23 

8.0 

3-27 

13.0 

5-31 

18.0 

7-33 

23.0 

9-36 

3-i 

1.27 

8.1 

3-31 

J3-1 

5-35 

18.1 

7-37 

23.I 

9.40 

3-2 

1.28 

8.2 

3-35 

13.2 

5-39 

18.2 

7.41 

23.2 

9-44 

3-3 

1.36 

8-3 

3-39 

J3-3 

5-43 

18.3 

7-45 

23-3 

9.48 

3-4 

1.40 

8.4 

3-43 

13-4 

5-47 

!8.4 

7-49 

23-4 

9-52 

3-5 

i-45 

8-5 

3-47 

*3-5 

5-5i 

18.5 

7-53 

23-5 

9-56 

3-6 

1.49 

8.6 

3-51 

13-6 

5-55 

18.6 

7-57 

23.6 

9.60 

3-7 

I-S3 

8.7 

3-55 

13-7 

5-59 

18.7 

7.61 

23-7 

9.64 

3-8 

J-57 

8.8 

3-6o 

13.8 

5-63 

18.8 

7-65 

23-8 

9.68 

3-9 

i.  60 

8.9 

3-64 

J3-9 

5-67 

18.9 

7.69 

23-9 

9.71 

4.0 

1.64 

9.0 

3-68 

14.0 

5-72 

19.0 

7-74 

24.0 

9-74 

4.1 

1.68 

9.1 

3-72 

14.1 

5.76 

19.1 

7-78 

24.1 

9.78 

4.2 

1.72 

9-2 

3-76 

14.2 

5-8o 

19.2 

7.82 

24.2 

9.82 

4-3 

1.77 

9-3 

3-8o 

14-3 

5-84 

19-3 

7.86 

24-3 

9.86 

4-4 

1.81 

9.4 

3-84 

14.4 

5-88 

19.4 

7.90 

24.4 

9.90 

4-5 

1-85 

9-5 

3-88 

14-5 

5-92 

19-5 

7-94 

24-5 

9-94 

4-6 

1.89 

9.6 

3-92 

14.6 

5-96 

19.6 

7.98 

24.6 

9.98 

4-7 

i-93 

9-7 

3-96 

14.7 

6.00 

19.7 

8.02 

24.7 

10.02 

4-8 

1.97 

9-8 

4.01 

14.8 

6.04 

19.8 

8.06 

24.8 

10.06 

4-9 

2.01 

9-9 

4-05 

14.9 

6.08 

19.9 

8.10 

24.9 

IO.  IO 

*-o 

2.0S 

TO.O 

4.09 

15.0 

6.12 

20.0 

8.14 

25.0 

10.  14 

COPPER. 


105 


Cc. 

%Cu. 

Cc. 

%Cu. 

Cc. 

%Cu. 

Cc. 

%Cu. 

Cc. 

%Cu 

25-1 

10.18 

30.1 

12.06 

35-1 

14.06 

40.  i 

16.04 

45-i 

18.04 

25.2 

10.22 

30.2 

12.12 

35-2 

14.  10 

40.2 

16.08 

45-2 

18.08 

2S-3 

10.26 

3°-3 

12.  14 

35-3 

14.14 

40.3 

16.  12 

45-3 

18.12 

25-4 

10.30 

30-4 

12.  l8 

35-4 

14.18 

40.4 

16.16 

45-4 

18.16 

2$-5 

10-34 

30-5 

12.22 

35-5 

14.22 

40-5 

16.20 

45-5 

18.20 

25.6 

10.38 

30.6 

12.26 

35-6 

14.26 

40.6 

16.24 

45-6 

18.24 

25-7 

10.42 

3°-7 

12.30 

35-7 

14-3° 

40.7 

16.28 

45-7 

18.28 

25-8 

10.46 

3°-8 

12-34 

35-8 

!4-34 

40.8 

16.32 

45-8 

18.32 

25-9 

10.50 

3°-9 

12.38 

35-9 

14-38 

40.9 

16.36 

45-9 

18.36 

26.0 

IO-53 

31-0 

12.42 

36.0 

14.42 

41.0 

16.40 

46.0 

18.40 

26.1 

10.56 

3i-i 

12.46 

36.1 

14-46 

41.1 

16.44 

46.  i 

18.44 

26.2 

10.  60 

31.2 

12.50 

36.2 

14.50 

41.2 

16.48 

46.2 

18.48 

26.3 

10.64 

3i-3 

12-54 

36-3 

J4-54 

41-3 

16.52 

46.3 

18.52 

26.4 

10.68 

3i-4 

12.58 

36.4 

14-58 

41.4 

16.56 

46.4 

18.56 

26.5 

10.72 

3J-5 

12.62 

36-5 

14.62 

41-5 

16.60 

46.5 

18.60 

26.6 

10.  76 

31-6 

12.66 

36.6 

14.66 

41.6 

16.64 

46.6 

18.64 

26.7 

10.80 

31-7 

12.70 

36-7 

14.70 

41.7 

16.68 

46-7 

18.68 

26.8 

10.84 

31-8 

12.74 

36.8 

14.74 

41.8 

16.  72 

46.8 

18.72 

26.9 

10.88 

31-9 

12.78 

36-9 

14.78 

41.9 

16.76 

46.9 

18.76 

27.0 

10.92 

32.0 

12.82 

37-0 

14.82 

42.0 

16.80 

47-o 

18.80 

27.1 

10  -95 

32.1 

12.86 

37-i 

14-87 

42.1 

16.84 

47-i 

18.84 

27.2 

10.98 

32.2 

12.90 

37-2 

14.91 

42.2 

16.88 

47-2 

18.88 

27.3 

11.02 

32.3 

I2-95 

37-3 

14-95 

42.3 

16.92 

47-3 

18.92 

27.4 

1  1.  06 

32-4 

12.99 

37-4 

14-99 

42.4 

16.96 

47-4 

18.96 

27-5 

II.  IO 

32-S 

13.04 

37-5 

15-03 

42.5 

16.99 

47-5 

19.00 

27.6 

11.14 

32.6 

13.08 

37-6 

15-07 

42.6 

17.04 

47-6 

19.04 

27.7 

ii.  18 

32-7 

13.12 

37-7 

15.11 

42.7 

17.08 

47-7 

19.08 

27.8 

11.22 

32.8 

13.16 

37-8 

I5-I3 

42.8 

17.12 

47-8 

19.  12 

27.9 

11.26 

32-9 

13.20 

37-9 

15.16 

42.9 

17.16 

47-9 

I9.l6 

28.0 

11.30 

33-o 

13^3 

38.0 

15.20 

43-o 

17.20 

48.0 

19.20 

28.1 

XI-33 

33-i 

J3-27 

38.i 

15.24 

43-i 

17.24 

48.1 

19.24 

28.2 

IJ-37 

33-2 

13-31 

38-2 

15.28 

43-2 

17.28 

48.4 

19.28 

28.3 

11.41 

33-3 

*3-35 

38.3 

I5-32 

43-3 

17.32 

48.3 

19.32 

28.4 

11.44 

33-4 

13-39 

38.4 

I5-36 

43-4 

17.36 

48.4 

19.36 

28.5 

11.48 

33-5 

J3-43 

38.5 

15.40 

43-5 

17.40 

48.5 

19.40 

28.6 

11.51 

33-6 

T3-47 

38.6 

15-44 

43-6 

17.44 

48.6 

19.44 

28.7 

«-5S 

33-7 

J3-51 

38.7 

15.48 

43-7 

17.48 

48.7 

19.48 

28.8 

n-59 

33-8 

J3-55 

38-8 

I5-52 

43-8 

I7-52 

48.8 

19.52 

28.9 

ii  .60 

33-9 

x3-59 

38-9 

IS-S6 

43-9 

17-56 

48.9 

19.56 

29.0 

11.65 

34-o 

x3-63 

39-o 

15.60 

44.0 

17.60 

49.0 

19.60 

29.1 

11.69 

34-1 

13-67 

39-i 

15.64 

44.1 

17.64 

49-1 

19.64 

29.2 

"•73 

34-2 

I3-7I 

39-2 

15.68 

44-2 

17.68 

49-2 

19.68 

29-3 

11.77 

34-3 

*3-75 

39-3 

I5-72 

44-3 

17.72 

49-3 

19.72 

29.4 

ii.  81 

34-4 

13-79 

39-4 

I5-76 

44-4 

17.76 

49-4 

19.76 

29-5 

11.85 

34-5 

13-83 

39-5 

15.80 

44-5 

17.80 

49-5 

19.80 

29.6 

11.88 

34-6 

13-87 

39-6 

15.84 

44-6 

17.84 

49-6 

19.84 

29-7 

11.92 

34-7 

i3-9i 

39-7 

15.88 

44-7 

17.88 

49-7 

19.88 

29.8 

11.94 

34-8 

*3-95 

39-8 

I5-92 

44.8 

17.92 

49-8 

19.92 

29.9 

11.98 

.34-9 

13-99 

39-9 

15.96 

44-9 

17.96 

49-9 

19.96 

30.0 

12.02 

.^.0 

14.03 

40.0 

16.00 

45.0 

18.00 

50.0 

20.00 

106  TECHNICAL  METHODS   OF    ORE  ANALYSIS. 

Owing  to  the.  slight  error  introduced  by  the  solubility  of 
cuprous  thiocyanate,  Guess  titrates  with  a  permanganate  solution 
of  the  exact  strength  i  cc.  =0.010  gram  Fe,  and  makes  use  of  the 
accompanying  table,  which  has  been  carefully  prepared  after 
long  comparison  with  the  electrolytic  method  on  the  same  samples. 

With  low-grade  material,  where  2  grams  are  taken  for  assay, 
the  error  may  be  neglected  and  the  copper  factor  deduced  as  0.2 
of  the  iron  value. 

19.  Guess'  Electrolytic  Method  for  Ores,  etc. — Mr.  G.  A. 
Guess  observed,  in  the  course  of  some  electrolytic  copper  work, 
that  a  "nitro"  preparation,  formed  by  the  action  of  strong  nitric 
acid  on  a  certain  petroleum  product,  when  added  to  the  usual 
nitric  acid  electrolyte,  permitted  the  employment  of  a  strong 
current,  with  a  corresponding  shortening  of  the  time  of  deposi- 
tion, without  injuring  the  reguline  nature  of  the  deposit.  Thus 
the  usual  8  to  12  hours  was  reduced  to  3.  At  the  same  time  it 
was  found  that  even  large  amounts  of  arsenic  and  antimony  did 
not  interfere  and  the  deposited  copper  remained  bright  and  un- 
contaminated. 

The  following  are  the  details  of  the  method: 

The  Nitro  Compound* — Heat  very  gently  a  mixture  of  about 
10  grams  of  vaseline  and  100  cc.  of  strong  nitric  acid.  When 
all  action  has  ceased,  dilute  to  about  300  cc.  and  allow  to  stand 
for  24  hours.  After  filtering  the  straw-colored  liquid  it  is  ready 
for  use. 

The  Electrodes. — These  are  of  the  Guess-Haul  tain  design  and 
are  made  of  o.ooi-inch  platinum  foil.  The  cathode  is  12.5  cm. 
long  and  is  divided  into  a  blade  4  cm.  wide  and  6.25  cm.  long, 
and  a  central  tongue  0.7  cm.  wide  and  6.25  long,  the  immersion 
area  being  50  sq.  cm.  and  weight  1.5  grams.  The  blade  is  first 

*  Modification  of  Messrs.  Cavers  and  Chadwick.     Eng.  and  Min.  Jour.,  Vol. 
89>  954. 


COPPER.  jo; 

sand-blasted  and  then  corrugated  lengthwise,  in  order  to  impart 
the  necessary  rigidity.  The  sand-blasting  is  to  permit  a  firmer 
adhesion  of  the  deposited  copper,  which  is  otherwise  liable  to 
fly  off  during  the  final  drying. 

The  anodes  are  12.5  cm.  long  and  0.5  cm.  wide  with  a  median 
corrugation.  Three  electrodes  are  used  in  each  cell;  one  cathode 
in  the  middle  and  one  anode  on  each  side  of  the  cathode.  These 
electrodes  are  connected  to  slotted  aluminum  terminals,  in  which 
they  are  held  by  contact  pressure.  The  terminals  are  f-inch 
rods,  projecting  2  inches  horizontally  in  front  of  the  wall  of  the 
cabinet;  at  the  back,  the  middle  electrode  (cathode)  is  con- 
nected with  one  pole  of  the  current,  and  the  two  outer  ones  (anodes) 
with  the  other  pole. 

The  Procedure. — Weigh  the  ore  into  a  tall  narrow  beaker  of 
about  200  cc.  capacity,  suitable  for  the  electrolysis.  Digest  with 
7  cc.  of  nitric  acid  and  boil  until  the  red  fumes  are  expelled. 
Add  about  -|  cc.  of  the  prepared  nitro  compound,  nearly  fill  the 
beaker  with  water  and  allow  to  stand  and  settle  for  a  moment. 
Insert  the  electrodes  and  electrolyse  with  a  current  of  1.5  am- 
peres for  3  hours. 

There  should  be  no  evolution  of  gas  whatever  at  the  cathode 
during  the  electrolysis.  Gas  is  frequently  evolved  when  the 
current  is  first  turned  on,  but  if  turned  off  for  a  second  and  then 
on  again,  the  bubbles  should  cease.  Gas  may  again  appear  at 
the  end  of  three  hours,  when  the  assay  is  finished. 

The  cathode  with  the  deposited  copper  is  finally  remove:!, 
dried,  and  weighed  in  the  usual  manner  (10). 

20.  The  Colorimetric  Determination  of  Copper.* — The  colon- 
metric  method  is  applicable  only  in  the  case  of  products  contain- 
ing small  amounts  of  copper,  such  as  slags  and  tailings.  It  is 

*  From  papers  by  F.  W.  Traphagen,  Western  Chem.  and  Met.,  VI,  148,  and 
Arthur  Austin,  Western  Chem.  and  Met.,  VI,  309. 


Io8  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

based  upon  the  depths  of  color  produced  by  cupro-ammonium 
nitrate,  and,  with  proper  precautions,  it  is  a  delicate  and  accurate 
means  of  determining  small  percentages  of  copper.  To  secure 
accuracy  it  is  necessary  to  have  the  conditions  under  which  the 
comparison  or  standard  solution  was  obtained,  and  that  of  the 
sample  under  examination,  as  nearly  identical  as  possible.  Hence, 
instead  or  preparing  the  standards  with  known  quantities  of  pure 
copper  only,  the  various  other  impurities  accompanying  the 
copper  in  the  sample  are  simulated,  by  using  tailings,  blast  or 
reverberatory  slags,  of  known  copper  content  in  making  up  the 
standard  comparison  solutions.  The  following  methods  are 
modifications  of  the  method  of  Thorn  Smith.  They  were  devel- 
oped and  are  used  in  the  laboratory  of  the  Anaconda  Copper 
Mining  Company. 

Preparation  of  Standards. 

Blast  Slags. — Take  3  grams  of  sample  on  which  the  copper 
has  been  determined  electrolytically,  cover  with  water,  add  10  cc. 
of  nitric  acid  and  i  cc.  of  hydrochloric  acid  and  heat  a  few 
minutes  on  the  steam-bath.  Dilute  the  mixture,  after  heating, 
with  100  cc.  of  water,  add  dilute  ammonia  in  slight  excess  and 
filter  into  a  colorimetric  bottle.  Wash  until  the  filtrate  fills  the 
bottle  to  the  mark.  If  the  electrolytic  copper  on  this  sample  was 
0.20  per  cent.,  this  standard  is  called  "B-2."  To  prepare  "6-3" 
add  0.003  gram  of  copper  to  another  3  grams.  "6-4"  is  pre- 
pared by  the  addition  of  0.006  gram  of  copper,  and  "6-5"  by 
adding  0.009  gram  of  copper,  the  copper  being  always  added 
before  the  ammonia,  and  the  samples  treated  as  in  the  prepara- 
tion of  "B-2."  If  samples  low  enough  in  copper  to  prepare  the 
lowest  standards  are  not  at  hand,  all  the  copper  may  be  removed 
electrolytically  and  then  sufficient  of  a  standard  copper  solution 
added  for  the  required  standard. 


COPPER. 


109 


Tailings.  —  Heat  i  gram  of  the  sample  on  the  steam-bath  with 
5  cc.  of  nitric  acid  and  a  pinch  of  potassium  chlorate.  Dilute, 
filter  and  wash  as  for  slags.  If  the  electrolytic  copper  on  this 
sample  was  0.50  per  cent.,  the  standard  is  called  "T~5."  To 
prepare  "T-6"  add  o.ooi  gram  of  copper  to  another  gram  sample; 
0.002  gram  for  "T-y";  0.003  gram  for  "T-8;"  0.005  gram  for 
"T-io." 

Reverberatory  Slags. — Take  2  grams  of  sample,  add  10  cc.  of 
hydrochloric  acid  and  2  cc.  of  nitric  acid.  Heat,  dilute,  add 
ammonia,  filter  and  wash  as  for  blast  slags.  If  the  electrolytic 
copper  on  this  sample  was  0.30  per  cent.,  this  standard  is  called 
"R~3."  For  "R-4"  add  0.002  gram  of  copper  to  another  2 
grams  of  sample.  Add  0.004  gram  for  "R-5,"  0.006  for  uR-6," 
and  so  on.  Treat  each  as  in  the  preparation  of  "R-3." 

A  set  of  standards  being  prepared  as  above,  another  set  of 
bottles  is  arranged,  each  bottle  being  filled  almost  to  the  mark 
with  water  and  10  cc.  of  ammonia.  A  standard  solution  of  cop- 
per, containing  o.ooi  gram  of  copper  to  the  cubic  centimeter,  is 
run  into  each  from  a  burrette  until  the  color  produced  exactly 
matches  a  corresponding  standard  prepared  as  above.  The 
burette  reading  is  carefully  noted  in  each  case. 

The  following  results  were  thus  obtained: 


B-2  required 

4.4  cc. 

R-2  requ 

tred    3.2  cc. 

T-3  reqi 

red  2.8  cc. 

B-3        " 

6.7  cc. 

R-3      ' 

4.6  cc. 

T-4 

3.8  cc. 

B-4        " 

9.1  cc. 

R-4        ' 

6.1  cc. 

T-5 

4-7  cc. 

B-5        " 

II.  I  CC. 

R-5      ' 

7.9  cc. 

T-6 

5-7  cc. 

R-6 

9.7  cc. 

T-7 

6.6  cc. 

R-7      ' 

11.4  cc. 

T-8 

7.6  cc. 

R-8        '          13.2  cc. 

T-9 

8.5  cc. 

T-io 

9-5  cc. 

By  the  use  of  this  table  standards  may  be  rapidly  prepared. 


no  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

Determination   of  Copper. 

Treat  blast  slags,  reverberatory  slags  and  tailings  exactly  as 
described  in  "Preparation  of  Standards"  and  match  the  nitrates 
with  the  standards. 

Details  of  Operation.  —  Except  in  the  case  of  converter 
slag  (of  which  0.5  gram  is  taken)  all  portions  are  i,  2,  or  3 
grams. 

Tailings  are  weighed  into  No.  i  beakers,  100  cc.  capacity, 
and  slags  into  No.  2  beakers,  200  cc.  capacity. 

Tailings  are  treated  with  nitric  acid  and  a  pinch  of  potas- 
sium chlorate,  set  upon  the  steam-plate  and  left  for  half  an  hour. 
The  addition  of  nitric  acid  should  be  regulated  so  as  to  leave 
about  5  cc.  after  treatment  on  the  hot  plate.  After  the  hot  plate 
treatment  about  25  to  30  cc.  of  cold  water  are  added  to  the 
beakers  and  they  are  then  placed  in  front  of  the  color  bottles 
which  have  been  previously  arranged.  These  color  bottles  are 
of  square  shape,  to  allow  of  easy  and  safe  handling,  and  are 
made  of  clear  white  glass.  They  are  7^  inches  high,  with  a 
body  2 J  inches  in  diameter  and  a  short  neck  about  if  inches 
in  diameter,  i :  i  ammonia  is  added  to  the  beakers  in  such 
quantity  as  to  give  about  the  same  excess  as  is  used  in  the  stand- 
ards. Ribbed  funnels  4!  inches  in  diameter  are  set  in  the 
mouths  of  the  bottles,  and  provided  with  niters  i8|  cm.  in  diam- 
eter. The  contents  of  the  beakers  are  now  poured  "clean"  into 
the  niters.  The  beakers  are  washed  once  with  warm  water, 
which  is  then  poured  through  the  niters,  and,  after  draining, 
the  precipitate  in  each  filter  is  given  one  good  wash  with  warm 
water.  The  funnels  are  now  removed  and  the  bottles  are  filled 
up  to  the  standard  marks  with  water.  The  larger  bulk  of  solu- 
tion before  filtering  and  the  greater  amount  of  wash  water  required 
cause  the  mark  on  the  slag  bottles  to  be  higher  than  that  on  the 


COPPER.  in 

tailings.  On  the  described  bottle  the  tailings  mark  will  come 
about  half  way  up,  and  the  slag  mark  will  be  near  the  top. 
The  tests,  when  ready,  are  matched  against  the  standard 
colors  arranged  in  a  color  stand.  The  latter  is  made  of  wood, 
painted  white,  and  faces  a  window.  Each  standard  bottle 
is  in  a  separate  compartment,  so  as  not  to  be  affected  by 
the  color  of  an  adjacent  standard.  In  making  comparisons 
the  standard  and  the  unknown  should  be  at  equal  distances 
from  the  partitions,  as  the  latter  have  a  slight  effect  on  the 
color. 

Results  are  read  and  reported  to  the  nearest  0.05  per  cent, 
by  reading  between  the  standards,  which  are  graduated  to  o.i 
per  cent. 

Reverberatory  and  blast  slags  require  different  treatment. 
Blast  slags  decompose  easily;  reverberatory  slags  are  best  decom- 
posed by  first  adding  hydrochloric  acid,  and  then,  after  digestion 
for  a  few  minutes  on  the  steam-plate,  making  an  addition  of 
nitric  acid.  A  little  water  added  before  the  acid,  so  as  to  make 
a  paste,  will  prevent  undecomposed  slag  from  sticking  to  the 
beaker  bottom. 

Reverberatory  slags,  and  also  converter  slags,  should  be 
allowed  about  three-quarters  of  an  hour  on  the  steam-plate, 
and,  when  taken  up  with  water,  they  require  a  good  stirring 
with  a  rubber  " policeman."  The  amount  of  iron  and  silica  is 
large,  and  the  dilute  ammonia  should  be  added  while  stirring, 
so  as  best  to  determine  the  required  excess. 

Sometimes  the  color  produced  in  a  test  has  a  greenish  tinge, 
and  the  test  is  then  apt  to  be  read  too  high.  Heath  states  that 
this  may  be  due  to  the  presences  of  organic  matter,  which 
impairs  the  complete  precipitation  of  ferric  hydroxide  by  ammo- 
nia. If  the  green  tint  is  too  pronounced  the  sample  should  be 
ignited. 


112  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

Standards  of  low  copper  content  seem  to  preserve  their  color 
best  with  a  small  excess  of  ammonia,  5  cc.  Those  of  higher 
copper  content  require  10  to  20  cc.  excess.  The  sample  to  be 
matched  should  be  as  near  like  the  standard  in  all  respects  as 
possible. 


CHAPTER  XIV. 

FLUORINE. 

i.  Kneeland's  Method  for  the  Determination  of  Fluorine  in 
Ores  and  Slags.* —  Fuse  0.5  or  i  gram  of  the  material  (according 
to  the  supposed  amount  of  fluorine  present)  in  a  porcelain 
crucible  with  ten  times  its  weight  of  a  mixture  of  equal  parts  of 
sodium  carbonate  and  potassium  carbonate  until  the  whole 
mass  is  in  quiet  fusion.  Raise  the  heat  to  bright  red  and  pour 
into  an  iron  mold,t  saving  the  crucible.  Cool,  break  up  the 
crucible  into  small  pieces,  and  transfer  along  with  the  fused 
mass  to  a  6-inch  agate-ware  casserole  (agate-ware  is  preferable 
to  porcelain  as  diminishing  the  liability  to  subsequent  "  bump- 
ing ").  Add  200  cc.  of  distilled  water  and  digest  for  one  hour 
at  a  temperature  near  the  boiling-point,  breaking  up  the  fused 
lump  with  a  thick  glass  rod.  If,  at  the  end  of  this  time,  any  unde- 
composed  lumps  are  noticed,  remove  them  with  the  pincers  and 
grind  them  in  an  agate  mortar  and  wash  back  into  the  casserole 
with  hot  water. 

Now  boil  for  10  minutes  and  filter  through  a  loose  filter  }  into 
a  beaker  of  about  i  liter  capacity.     Wash  first  with  hot  water, 

*  E.  Kneeland,  Eng.  and  Min.  Jour.,  LXXX,  1212. 

t  Instead  of  an  iron  mold,  a  clean  metallic  dish  floating  on  water  may  be  used. 
(A.H.  L.) 

t  For  this  filtration  I  would  suggest  a  thick  wad  of  absorbent  cotton  placed  in 
a  funnel  and  wetted.  (A.  H.  L.) 

"3 


H4  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

tnen  with  a  hot  solution  of  ammonium  carbonate.  The  residue 
is  now  discarded.  Add  to  the  nitrate  10  gr?ms  of  ammonium 
carbonate  and  boil  5  minutes,  and  afterwards  allow  to  stand  in 
the  cold  for  two  hours.  Filter  through  a  loose  filter  (see  last  foot- 
note) into  a  6-inch  agate-ware  casserole  (decanting  as  much  as 
possible  of  the  fluid)  and  wash  with  cold  water  once  or  twice. 
In  order  to  eliminate  the  final  traces  of  silica,  add  20  cc.  of  an 
emulsion  of  zinc  oxide  in  ammonia  (cf.  xxiv,  16),  and  boil,  w'th 
the  casserole  uncovered,  until  the  odor  of  ammonia  is  no  longer 
detected. 

Filter  into  a  No.  5  beaker  and  wash  with  hot  water.  To  the 
filtrate  add  a  solution  of  calcium  chloride,  while  stirring  with  a 
rubber-tipped  glass  rod,  until  no  more  precipitate  is  formed. 
Allow  the  precipitate  to  subside,  and  filter,  washing  with  hot 
water.  Test  the  filtrate  for  carbonates  and  fluorine  with  a  few 
drops  of  the  calcium  chloride  solution.  Now  transfer  the  pre- 
cipitate along  with  the  filter-paper  to  a  platinum  dish  of  suitable 
size.  Dry  first,  then  ignite  at  a  red  heat  for  20  minutes.  Cool, 
and  disintegrate  the  mass  with  hot  water.  Add  acetic  acid  until 
the  solution  is  clear  and  evaporate  to  dryness,  being  careful  not 
to  scorch.  Now  moisten  again  with  acetic  acid  and  then  evap- 
orate until  the  odor  of  acetic  acid  is  no  longer  perceptible. 

Wash  the  mass  into  a  No.  3  beaker  with  hot  water,  add  hot 
water  until  the  calcium  acetate  is  all  dissolved,  then  about 
150  cc.  more  and  stir.  Digest  for  a  few  minutes  at  a  gentle 
heat  and  filter,  washing  first  with  hot  water,  then  with  hot  am- 
monium  chloride  solution,  and  again  with  hot  water.  Transfer 
the  precipitate  and  filter-paper  to  a  platinum  dish,  dry,  and 
ignite.  Cool,  moisten  with  cold  water,  add  6  cc.  of  strong  sul- 
phuric acid,  and  heat  for  a  few  minutes.  Cool,  dilute,  and 
transfer  the  contents  of  the  dish  to  a  No.  2  beaker.  Add  5  grams 
of  ammonium  chloride,  boil  for  a  few  minutes,  cool,  and  add  an 


FLUORINE.  IJ5 

excess  of  strong  ammonia  water.  Then  add  2  or  3  cc.  of  strong 
hydrogen  peroxide  solution,  boil  and  filter.  Precipitate  the 
calcium  from  the  filtrate  with  ammonium  oxalate  and  determine 
the  calcium  as  CaO  in  the  usual  manner  by  titration  with  per- 
manganate (x,  4).  Calculate  the  CaO  to  CaF2,  from  which  the 
amount  of  fluorine  can  readily  be  calculated. 

To  calculate  CaO  to  CaF2  multiply  the  percentage  of  CaO 
found  by  1.392.  Multiply  the  percentage  of  CaF2  found  by 
0.4865  to  obtain  the  percentage  of  fluorine. 

(It  is  simpler  to  use  the  permanganate  factor  for  fluorine. 
This  may  be  obtained  by  multiplying  the  factor  for  CaO  by 
0.6770.— A.  H.  L.) 


2.  Penfield's  Volumetric  Method  for  Fluorine  in  Fluor- 
spar.*— Solutions  and  Reagents. — One-fifth  normal  Sodium 
Hydroxide  solution,  prepared  and  standardized  in  the  usual 
manner. 

i  cc.  of  this  solution  =  0.02 34  gram  CaF2. 
"     "    "         "       =0.0114  gram  F. 

Alcoholic  Potassium  Chloride  solution,  prepared  by  dissolving 
30  grams  of  potassium  chloride  in  100  cc.  of  water  and  adding 
100  cc.  of  alcohol.  20  cc.  of  the  solution  are  used  for  each  deter- 
mination. 

Lacmoid  Indicator,  prepared  by  dissolving  0.2  gram  of  lac- 
moid  (resorcin  blue)  in  100  cc.  of  alcohol.  This  indicator  is 
red  with  acids  and  blue  with  alkalies. 

Powdered   Silica.     Ignited  powdered   quartz   or  precipitated 

*  This  description  of  Penfield's  method  is  from  The  Chemical  Engineer,  Vol. 
HI,  p.  65. 


n6 


TECHNICAL  METHODS  OF  ORE    ANALYSIS. 


silica   will  either  of  tnem  answer  the  purpose,  provided  they 
are  free  from  fluorine. 

Sulphuric  Acid.  This  must  be  concentrated.  It  is  best  to 
heat  it  in  a  well-annealed  flask  until  it  fumes  strongly  and  then 
cool,  stoppering  the  flask  with  a  perforated  cork  carrying  a  6-inch 
piece  of  capillary  tube,  until  the  acid  is  cold,  and  then  with  a 
solid  rubber  stopper. 


FIG.  16. 

The  apparatus  is  shown  in  the  diagram  and  consists  of  a 
we'il- annealed  25o-cc.  flask  d  closed  by  a  2-hole  rubber  stopper. 
Through  one  of  these  holes  passes  a  funnel,  c,  which  can  be  easily 
made  by  joining  a  piece  of  glass  tubing  on  to  a  calcium  chloride 
tube  to  form  a  long  enough  stem  to  reach  nearly  to  the  bottom 


FLUORINE.  ii? 

of  the  flask.  The  funnel  is  filled  with  dry  glass  beads,  and  is 
closed  by  a  stopper,  in  the  single  hole  of  which  is  inserted  a  cal- 
cium chloride  tube  filled  with  dry  granular  soda-lime. 

The  rubber  tube  a  connects  the  apparatus  with  the  source 
of  a  current  of  air,  which  later  can  be  shut  off  by  the  Hoffmann 
clamp  as  shown.  In  the  second  hole  of  the  flask- stopper  a  con- 
denser-tube ej*  bent  as  shown,  is  inserted.  This  is  made  by 
blowing  a  bulb  in  a  piece  of  glass  tubing  (6  mm.  in  diameter), 
and  is  kept  cool  by  immersion  in  a  beaker  of  cold  water.  The 
test-tube  /  is  connected  to  e  by  a  rubber  joint  as  shown,  and 
is  provided  with  inlet  and  outlet  tubes,  the  latter  being  connected 
with  the  inlet  tube  of  another  test-tube,  g.  The  test-tube  / 
is  8  inches  high,  while  g  is  only  6  inches.  Both  tubes  are  held 
upright  by  a  small  block  of  wood,  h,  bored  with  holes  to  fit  the 
tubes. 

3.  Determination.  —  Have  the  flask  and  condenser-tube  e 
and  the  entrance-tube  to  the  test-tube  /  thoroughly  dry.  Pour 
about  J  inch  of  mercury  into  the  test-tube  /,  and  on  top  of  this 
25  cc.  of  the  potassium  chloride  solution.  Half  fill  the  test-tube  g 
also  with  this  solution. 

Now  weigh  into  an  agate  mortar  0.2  to  0.5  gram  of  the  finely 
powdered  sample,  place  the  mortar  on  a  piece  of  black  glazed 
paper  and  carefully  mix,  by  gentle  rubbing  with  the  pestle,  the 
sample  of  fluorspar  with  10  times  its  weight  of  powdered  silica. 
After  mixing,  transfer  to  the  flask,  cork  the  latter  and  connect 
up  the  apparatus  as  shown.  Pour  25  cc.  of  concentrated  sul- 
phuric acid  through  the  funnel  c  (and  the  glass  beads)  into  the 
flask  d.  As  soon  as  the  acid  is  poured  into  the  funnel,  close  the 
latter  with  the  stopper  and  guard- tube  b.  Place  the  flask  in  a 
bath  of  paraffin  and  heat  to  about  160°  C.  for  one  or  two  hours. 

*  This    tube    serves    to    remove    any  sulphuric   acid    mechanically   carried 
over   with    the  gas. 


Il8  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

A  slow  current  of  air  is  passed  through  the  apparatus  during 
this  time.  The  test-tube  /  is  then  disconnected  from  the  con- 
denser-tube et  and  its  contents  together  with  that  of  g  are  rinsed 
into  the  beaker.  Any  pasty  silicic  acid  adhering  to  the  sides  of  / 
must  be  removed  with  a  stirring- rod,  for  otherwise  some  enclosed 
acid  will  escape  the  titration.  Add  a  drop  of  the  lacmoid  indi- 
cator to  the  contents  of  the  beaker,  and  titrate  the  mixture  with 
the  standard  alkali.  Calculate  the  percentage  of  fluorine,  as 
usual,  from  the  weight  of  sample  taken  and  the  number  of  cubic 
centimeters  of  alkali  required. 

The  process  depends  upon  the  fact  that  upon  treatment  of 
fluorides  with  sulphuric  acid  and  silica  the  following  reaction 
takes  place: 

2CaF2  +  2H2SO4  +  SiO2  =  2CaSO4  +  2H2O  +  SiF4. 

Upon  coming  in  contact  with  water,  the  silicon  fluoride  is 
decomposed  into  hydrofluosilic  and  silicic  acids: 

3SiF4  +  2H2O  =  2H2SiF6  +  SiO2. 

The  hydrofluosilicic  acid  unites  with  the  potassium  chloride, 
forming  potassium  silicofluoride  (insoluble  in  50  per  cent,  alcohol) 
,and  hydrochloric  acid: 

H2SiF6  +  2  KC1  =  K2SiF6  +  2HC1. 

The  hydrochloric  acid  set  free  is,  of  course,  titrated,  and 
as  3F2  =  2HC1,  i  cc.  of  >N/5  alkali  =  0.0114  grams  of  fluorine. 

Sufficient  alcohol  should  always  be  added  to  the  liquid  to  be 
titrated  to  have  at  least  fifty  per  cent,  present  by  volume,  other- 
wise the  silicofluoride  will  fail  to  be  completely  precipitated,  and, 
as  the  end-point  is  reached,  will  slowly  decompose  and  again 
cause  an  acid  reaction. 


CHAPTER    XV. 

IRON. 

1.  In  the  determination  of  iron  in  ores  and  metallurgical 
products    some    modification    of    either    the    permanganate    or 
dichromate   volumetric   method   is   ordinarily   employed.     Both 
methods  give  exact  results,  and  the  choice  of  the  one  to  use  usually 
depends  on  either  the  personal  preference  of  the  operator  or  the 
convenience  of  the  case  in  hand. 

The  following  modifications  of  these  methods  are  employed 
in  my  laboratory. 

2.  Permanganate  Method. — This   method   is   based   on   the 
following  reaction: 

ioFeSO4  +  2KMnO4  +  8H2SO4 

=  5Fe2(SO4)3  +  2MnSO4  +  K2SO4  +  H2O. 

The  ferrous  salt,  which  may  be  either  a  sulphate  or  a  chloride, 
is  oxidized  to  the  ferric  condition  by  the  permanganate,  which 
is  itself  decomposed  and  decolorized.  When  the  permanganate 
in  solution  is  added  gradually,  its  color  is  continually  destroyed 
as  long  as  any  ferrous  salt  remains,  but  as  soon  as  the  oxidation 
is  complete  the  addition  of  more  permanganate  imparts  a  per- 
manent pink  tint  to  the  liquid.  The  above  equation  shows  that 
it  requires  316.3  parts  of  potassium  permanganate  to  oxidize 

559  parts  of  iron  from  the  ferrous  to  the  ferric  condition.     To 

119 


120  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

make  a  standard  solution,  therefore,  so  that  i  cc.  shall  equal 
i  per  cent,  of  iron,  i.e.,  0.005  gram  when  0.5  gram  of  ore  is  taken 
for  assay,  we  solve  the  proportion 

316.3: 559  =#10.005. 

#  =  0.00283.  This  is  the  weight  of  permanganate  required 
in  i  cc.,  which  is  equivalent  to  2.83  grams  per  liter.  When  used 
for  iron  determinations,  the  solution  may  conveniently  be  made 
of  approximately  this  strength.  Its  exact  value  is  determined 
by  standardization. 

3.  There  are  three  common  methods  of  standardizing  the 
permanganate  solution: 

1.  By  metallic  iron  or  an  iron  solution  of  known  strength. 

2.  By  a  stable  ferrous  salt. 

3.  By  oxalic  acid  or  an  oxalate. 

I  have  found  the  metallic  iron  method,  when  carried  out  as 
described  below,  and  the  oxalic  acid  or  oxalate  method  to  give 
practically  identical  results,  and  I  ordinarily  use  the  latter  on 
account  of  its  simplicity.  The  stable  ferrous  salt  usually  employed 
is  ferrous  ammonium  sulphate.  As  ordinarily  obtainable  it  is  not 
a  sufficiently  reliable  basis  for  the  best  work. 

After  making  up  the  permanganate  solution  it  should  be 
allowed  to  stand  at  least  a  day  before  standardizing,  as  when 
first  prepared  it  is  constantly  changing  in  strength,  owing  to 
oxidation  of  the  organic  matter  always  present  in  the  liquid. 

4.  To  standardize  by  means  of  metallic  iron,  weigh  0.15- 
0.20  gram  of  very  finely  drawn  clean  iron  wire  and  dissolve  in 
an  8-oz.  flask  in  a  mixture  of  5  cc.  each  of  strong  nitric  and  hydro- 
chloric acids. 

Very  finely  drawn  polished  iron  wire  can  be  purchased  at  the 
supply  stores  marked  with  its  true  percentage  of  iron,  usually 
about  99.8.  Sutton  recommends  the  use  of  soft  "flower- wire,5' 


IRON.  121 

of  which  the  actual  percentage  of  iron  may  be  assumed  to  be 
99.6.  Pure  electrolytic  iron  in  granulated  form  is  also  to  be 
obtained.  It  has  the  advantage  of  dissolving  very  rapidly  in 
hydrochloric  or  dilute  sulphuric  acid,  and  is  said  to  keep  well 
without  oxidizing.  When  iron  wire  is  used  the  precaution  should 
be  taken  to  have  it  perfectly  clean  and  free  from  rust.  If  polished 
and  apparently  clean,  it  may  simply  be  drawn  through  a  piece 
of  filter-paper  held  in  the  hand  to  insure  freedom  from  dust  and 
grease,  but  if  at  all  oxidized  it  should  first  be  thoroughly  cleaned 
with  fine  emery-paper  or  cloth. 

5.  Having  placed  the  wire  in  the  flask,  best  in  a  snug  coil, 
add  the  acid  and  warm  the  mixture  gently.    The  wire  will  quickly 
dissolve.     Besides   effecting   a   rapid   solution   of  the   iron,    the 
aqua  regia  also  serves  to  oxidize  hydrocarbons  and  other  com- 
pounds,  due   to   impurities   in   the   wire,   that   would   otherwise 
consume  a  little  permanganate  in  the  titration.     When  the  wire 
has  dissolved  add  5  cc.  of  strong  sulphuric  acid  and  boil  over 
a  free  flame  (manipulating  the  flask  in  a  holder)  until  the  hydro- 
chloric and  nitric  acids  are  expelled  and  most  of  the  sulphuric 
also.     Allow  to  cool  and  add  30  cc.  of  cold  water,  10  cc.  of  strong 
hydrochloric  acid  and  i  cc.  of  5%  CuSO4  solution. 

6.  Now  add  6  grams  of  pure  granulated  zinc   (best  about 
2o-mesh).     This  should  be  roughly  weighed,  as  all  zinc  contains 
a  little  iron  and  the  error  thus  introduced  must  be  subsequently 
determined  and  allowed  for.     The  iron  is  reduced  from  the  ferric 
to  the  ferrous  condition  according  to  the  equation 

2FeCl3  +  Zn  =  2FeCl2  +  ZnCl2. 

Hydrogen  is  also  liberated  by  the  action  of  the  free  acid  on 
the   zinc.     The  copper  added  precipitates  arsenic. 

Allow  the   reaction  to   continue   until   the   solution   is  com- 


122  TECHNICAL  METHODS  OF   ORE   ANALYSIS, 

pletely  decolorized,*  heating,  if  necessary,  toward  the  end  if 
the  action  is  slow.  Now  dilute  the  mixture  in  the  flask  to 
within  about  an  inch  of  the  neck  with  cold  water.  This  will 
dissolve  whatever  zinc  remains  and  will  also  supply  the  solu- 
tion with  a  large  excess  of  sulphuric  acid.  The  latter  will 
counteract  the  otherwise  disturbing  influence  of  the  hydro- 
chloric acid  present  during  the  subsequent  titration  and  secure 
a  sharp  end-point.  Hydrochloric  acid  and  potassium  per- 
manganate mutually  deconpose  each  other  with  the  evolution 
of  chlorine  as  follows: 

2KMn04  4-  i6HCl  =  2KC1  +  2MnCl2  +  8H2O  +  loCl. 

When  this  takes  place  during  an  iron  titration,  the  amount  of 
permanganate  consumed  is  increased,  thus  producing  high  results, 
while  the  end-point  is  obscured  owing  to  the  continual  fading  of 
the  pink  tinge.  If,  however,  the  solution  is  cold,  largely  "diluted, 
and  contains  a  proper  excess  of  sulphuric  acid,  a  little  hydro- 
chloric acid  causes  no  trouble,  f 

7.  When  the  zinc  is  nearly  all  dissolved  the  mixture  should 
be  filtered.  Nearly  all  zinc  contains  lead  as  an  impurity,  and 
this  remains  behind  as  a  finely  divided  black  residue,  which 
would  cause  trouble  by  consuming  permanganate  if  not  filtered 
off.  As  the  solution  has  a  tendency  to  clog  a  filter  and  run  very 
slowly  it  is  better  to  filter  through  a  plug  of  absorbent  cotton 
placed  in  a  funnel  and  moistened.  Do  not  use  an  unnecessarily 
large  wad.  Place  it  in  the  funnel  so  that  the  under  side  is 

*  If  desired,  the  completion  of  the  reduction  may  be  determined  by  removing 
a  drop  of  the  liquid  with  a  glass  rod  and  touching  it  on  a  porcelain  plate  with  a 
drop  of  ammonium  thiocyanate  solution.  Any  ferric  iron  remaining  will  produce  a 
red  tinge. 

t  It  appears  to  make  a  very  slight  change  in  the  standard,  but  this  is  of  no 
consequence  in  technical  work,  as  iron  determinations  are  made  the  same  way. 


IRON. 


123 


smooth,  with  the  fibers  lying  horizontally.  If  the  latter  are 
allowed  to  string  downward  they  are  liable  to  obstruct  the  neck 
of  the  funnel  and  cause  a  slow  nitration.  The  proper  ar- 
rangement filters  rapidly  and  washes  easily.  Receive  the 
filtrate  in  a  4-inch  by  5-inch  glass  battery-jar  containing  an 
inch  or  two  of  water.  Wash  the  filter  and  residue  well  with 
cold  water. 

8.  Dilute  the  solution  in  the  battery-jar  with  cold  distilled 
water  to  about  700  cc.,  having  previously  placed  a  mark  on  the 
jar  at  that  point.     The  solution  is  now  ready  for  titration,  which 
should  be  proceeded  with  without  unnecessary  delay,  to  avoid 
oxidation  of  the  ferrous  iron  by  the  air.     Place  a  piece  of  white 
paper  under  the  jar,  in  order  that  the  color  change  may  be  ren- 
dered more  distinct,  and  run  in  the  permanganate  solution  from 
a  burette  while  stirring  the  mixture  with  a  glass  rod.     The  color 
of  the  permanganate  is  almost  instantly  destroyed  at  first,  but  as 
the  end-point  is  approached  a  less  rapid  decolorization  can  easily 
be  detected  if  the  permanganate  be  added  cautiously.     Proceed 
more  and  more  carefully,  finally  drop  by  drop,  until  a  very  faint 
permanent  pink  tinge  is  obtained.     The  reaction  being  now  com- 
plete, read  the  burette.     Another  drop  of  permanganate  should 
turn  the  solution  decidedly  pink. 

Before  calculating  the  standard  of  the  permanganate  it  is 
necessary  to  apply  a  correction  by  deducting  the  amount  of  per- 
manganate solution  required  to  produce  the  same  pink  tint  in  a 
solution  containing  no  dissolved  iron  wire,  but  otherwise  of  the 
same  volume  and  condition  and  containing  the  same  reagents. 
To  determine  this  correction  once  for  all  for  the  same  reagents 
proceed  as  follows: 

9.  Treat  6  grams  of  the  zinc  regularly  used,  in  an  8-oz.  flask, 
with  a  mixture  of  10  cc.  of  strong  hydrochloric  acid  and  25  cc. 
of  water  and  add  gradually  a  mixture  of  10  cc.  of  strong  sulphuric 


124  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

acid  and  20  to  30  cc.  of  water.  When  the  zinc  has  all  dissolved, 
dilute  with  cold  water  and  filter  through  absorbent  cotton  as 
described  for  the  standardization,  finally  titrating  with  perman- 
ganate precisely  as  before.  Note  the  amount  of  permanganate 
required  and  deduct  this  volume  from  the  burette  reading  of  all 
corresponding  iron  titrations. 

A  correction  is  sometimes  made  for  the  color  due  to  the  ferric 
salt  present  at  the  end  of  a  titration,  but  the  error  from  this  cause 
is  usually  negligible. 

10.  Having  now,  in  the  standardization  of  the  permanganate, 
taken  the  final  reading  of  the  burette  and  deducted  the  correc- 
tion, there  remains  only  to  divide  the  actual  weight  of  iron  in  the 
iron  wire  taken  by  the  number  of  cubic  centimeters  used  to  find 
the  value  of  i  cc.  in  iron. 

Example. — Weight  of  iron  wire  taken.  .....     o.  1725  gram 

Actual  weight  of  iron  (99.8%)  . .     0.1721     ' ' 

Burette  reading 34 . 90      cc. 

Correction  .  .  . o.  20      ' ' 


Corrected  reading 34-7°      cc. 

0.1721  -^-34.70  =  0.004961. 

This  is  the  weight  of  iron  in  grams  to  which  I  cc.  of  the  perman- 
ganate is  equivalent. 

On  the  basis,  then,  of  0.5  gram  of  ore  being  taken  for  assay, 
i  cc.  =  0.9922  per  cent,  of  iron. 

ii.  To  standardize  by  means  of  a  ferrous  salt,  ferrous  am- 
monium sulphate  is  commonly  used.  This  salt  has  the  compo- 
sition FeSO4(NH4)2SO4  +  6H2O.  It  contains  14.25  percent,  of 
iron,  although  it  is  frequently  assumed  to  contain  exactly  one- 
seventh  of  its  weight  of  iron.  Weigh  from  i  to  1.5  grams  of  the 


IRON.  125 

pure  salt  and  dissolve  in  a  battery- jar  in  700  cc.  of  cold  distilled 
water  acidified  with  10  cc.  of  strong  sulphuric  acid.  Titrate  at 
once  to  the  usual  pink  tint.  Make  a  blank  test  on  the  plain 
acidulated  water  to  determine  the  amount  of  permanganate  re- 
quired to  produce  a  tint  and  deduct  the  correction  thus  found 
from  the  former  reading.  Calculate  the  standard  as  above. 

12.  To  standardize  with  oxalic  acid  proceed  as  described  in 
x,  6,  and  determine  the  oxalic  acid  value  of  i  cc.  of  the  perman- 
ganate.    This  value  multiplied  by  0.8867  w^  giye  tne  ^on  factor. 
This  is  a  convenient  and  accurate  method,  and  is  the  one  usually 
employed  in  my  laboratory. 

13.  Treatment   of   an  Ore. — Weigh  0.5  gram  of  the  ore  and 
place  in  an  8-oz.  flask.     Decompose  with  acids  according  to  the 
nature  of  the  sample.     It  is  usually  best  to  begin  with  10  cc.  of 
strong  hydrochloric  acid  and  warm  gently  as  long  as  decom- 
position  appears   to   progress,   adding   more  acid   if  necessary. 
If  undecomposed  sulphides  remain,  add  5  cc.   of  strong  nitric 
acid   and   continue   the   heating.     Note   whether   the   insoluble 
residue  now  appears   white  or  discolored.     In   the   latter  case 
endeavor  to  effect  a  better  decomposition  by  continued  gentle 
heating   with   hydrochloric   acid.     Finally,   add   to   the   mixture 
(which  should  not  be  so  concentrated  as  to  contain  separated 
salts)  about  5  cc.  of  strong  sulphuric  acid  and  heat  the  flask, 
supported  in  a  holder,  over  a  free  flame  until  practically  all  the 
acid,  including  the  sulphuric,  is  expelled.*     Allow  to  cool,  add 
30    cc.  of  cold  water  and  10  cc.  of  strong  hydrochloric  acid,  and 
the  mixture  is  at  6nce  ready  for  the  reduction  of  the  iron  with 
zinc.     It  is  not  necessary  to  get  the  salts  into  solution  before 
adding  the  zinc.     They  will  dissolve  very  quickly  after  reduction 
begins. 

*  Nitric  acid  may  not  be  entirely  expelled  by  this  treatment  unless  all  nitrates 
are  in  solution  when  the  sulphuric  acid  is  added. 


126  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

If  hydrochloric  acid  alone  effects  a  solution  of  all  the  iron  in 
the  ore,  the  further  treatment  with  nitric  or  sulphuric  acid  is 
unnecessary.  In  such  a  case,  in  order  to  have  the  right  amount 
of  acid  finally  present,  boil  the  solution  nearly  to  dryness  and 
then  add  8  cc.  more  of  hydrochloric  acid.  Dilute  to  40  cc.  with 
cold  water  and  proceed  with  the  reduction. 

14.  Add   6  grams   of  pure   granulated  zinc    (2o-mesh)   and 
reduce  the  iron  precisely  as  described  for  the  standardization 
of  the  permanganate  by  the  metallic  iron  method  (6). 

When  the  reduction  is  complete,  dilute  with  cold  water  to 
within  about  an  inch  of  the  neck  of  the  flask  and  add  10  cc. 
of  strong  sulphuric  acid.  Besides  a  residue  of  lead  from  the  zinc 
itself,  reducible  metals  from  the  ore,  such  as  lead,  copper,  arsenic, 
etc.,  will  be  precipitated.  All  this  residue  must  be  removed. 
When  the  zinc  is  nearly  all  dissolved,  filter  the  mixture  through 
a  plug  of  moistened  absorbent  cotton  into  a  battery-jar,  as 
described  in  7,  washing  the  filter  well  with  cold  water.  Dilute 
to  700  cc.  and  titrate  at  once  with  permanganate,  as  described 
in  8.  After  reading  the  burette,  deduct  the  correction  previously 
determined  (9)  and  multiply  the  actual  number  of  cubic  centi- 
meters used  for  the  ore  by  the  percentage  value  of  i  cc.  for  iron. 
This  gives  the  percentage  of  iron  in  the  sample. 

15.  Effect  of  a  Large  Amount  of  Arsenic. — Ores  containing  a 
large  amount  of  arsenic  will  frequently  give  low  and  variable 
results,  and  the  titration  will  have  a  rather  quickly  fading  end- 
point.     Apparently,  some  arsenic  has  been  left  in  solution,  after 
the  reduction,   in   the  ic   condition,   and   this,   by  subsequently 
oxidizing  iron,  brings  the  results  low,  as  the  arsenious  acid  pro- 
duced is  only  very  slowly  acted  upon  by  the  permanganate. 
The  addition  of  cupric  sulphate  solution,   as  prescribed  in   5, 
usually   prevents   this   trouble   by   precipitating   any   arsenic   in 
solution.     The  zinc  alone  cannot  be  depended  upon  to  do  this. 


IRON. 


12? 


16.  Treatment  of  Silicates  and  Other  Refractory  Substances. 

— The  acid  treatment  just  described  will  serve  excellently  for  the 
decomposition  of  most  ores  treated  at  western  lead-smelters,  but 
silicates,  furnace  products,  refractory  oxides,  etc.,  are  frequently 
encountered  that  fail  to  thus  yield  up  all  their  iron.  In  the  pur- 
chase of  ores  for  lead-smelters  the  actual  total  iron  contents  are 
not,  as  a  rule,  absolutely  required,  but  only  what  is  obtained 
by  the  acid  treatment.  In  the  majority  of  cases  practically  all 
the  iron  is  thus  dissolved.  What  remains  is  classed  with  the 
insoluble  residue  or  "silica."  Whenever  the  total  iron  is  required 
the  material  must,  of  course,  be  completely  decomposed. 

17.  Silicates.— --Silicates,    or    mixed    material    containing   sili- 
cates,  may   be   decomposed   as   described   under   SILICA.     The 
nature  of  the  material  has  to  be  considered  in  deciding  upon 
the  best  course  to  pursue  and  the  matter  of  the  decomposition  is 
fully  explained  in  the  section  referred  to.     An  acid  solution  of 
the  iron  is  thus  finally  obtained.     If  in  two  portions,  as  the  result 
of  an  acid  treatment  followed  by  a  fusion  of  the  residue,  they 
should  be  united.     When  only  iron  is  to  be  determined  it  is 
usually  unnecessary  to  evaporate  to  dryness  to  remove   silica. 
Warm  the  solution  in  a  beaker,  add  a  little  bromine  water  if 
the  iron  is  not  fully  peroxidized,  and  then  precipitate  the  iron  as 
ferric    hydroxide    with    excess    of   ammonia.     Heat    to    boiling, 
allow  to  settle,  filter,  and  wash  thoroughly  with  hot  water.     With 
a  jet  from  the  wash-bottle  transfer  the  bulk  of  the  washed  pre- 
cipitate from  the  filter  to  a  beaker,  using  as  little  water  as  possible, 
and  then  place  the  beaker  under  the  funnel.     Pour  through,  the 
filter  a  hot  mixture  of  10  cc.  of  strong  hydrochloric  acid  and  10  cc. 
of  water,  so  as  to  dissolve  the  precipitate  still  remaining,  finally 
washing  the  filter  with  a  little  hot  water.     Warm  the  mixture 
in  the  beaker  to  dissolve  all  the  ferric  hydroxide,  concentrate  if 
necessary,  by  boiling,  to  about  30  cc.,  and  transfer  the  solution 


128  TECHNICAL   METHODS   OF    ORE  ANALYSIS. 

to  an  8-oz.  flask.     Reduce  with  zinc  and  continue  in  the  usual 
manner,  as  directed  in  14. 

18.  Decomposition  of  Silicates  by  Hydrofluoric  Acid. — Some- 
times the  iron  in  a  silicate,  or  a  silicious  residue  remaining  after 
acid  treatment,  can  be  quickly  dissolved  as  follows: 

Treat  the  substance  in  a  small  platinum  dish  with  equal 
parts  of  strong  pure  hydrochloric  and  hydrofluoric  acids.  Warm 
gently  until  decomposition  appears  complete,  adding  more  of 
the  acids  if  necessary,  and  then  add  about  3  cc.  of  dilute  sulphuric 
acid  (1:2)  and  evaporate  to  white  fumes.  To  the  cool  residue  add 
a  little  water  and  a  few  drops  of  hydrochloric  acid  and  warm  to 
effect  solution.  If  the  material  is  a  residue,  transfer  this  solution 
to  the  flask  containing  the  original  nitrate,  make  to  a  volume  of 
about  40  cc.,  reduce  with  zinc,  and  finish  as  usual  (14).  If  the 
material  is  the  ore  itself  the  operations  are  similar,  but  5  cc. 
of  hydrochloric  acid  must  be  added  before  reduction.  When 
nitric  acid  has  been  used  in  a  preliminary  treatment  it  should  be 
expelled  before  filtration  from  the  residue  (13).  The  solution 
for  reduction  should  have  a  volume  of  about  40  cc.  and  contain 
from  5  to  10  cc.  of  free  hydrochloric  acid. 

19.  Refractory   Oxides,    etc. — Treat  0.5   gram  of  the  finely 
ground  sample  with   10-15  cc.   of    strong  hydrochloric  acid  in 
an  8-oz.  flask.     Digest  at  a  very  gentle  heat,  adding  more  acid,  if 
necessary,  as  long  as  the  undissolved  residue  appears  to  be  appre- 
ciably attacked.     If  the  ore  contains  carbonaceous  matter,  add 
a  few  crystals  of  potassium  chlorate  to  oxidize  it.     Finally  boil  or 
evaporate  to  a  few  cubic  centimeters  and  then  dilute  with  10-15  cc- 
of  water  and  heat  to  boiling,  adding  a  few  drops  of  hydrochloric 
acid,  if  necessary,  to  dissolve  any  separated  basic  compounds. 
Filter  the  solution  through  a  small  filter  and  collect  the  filtrate 
in  an   8-oz.   flask.      Transfer   the   insoluble  residue  completely 
to  the  filter   and    wash    with  hot  water,  but  avoid  getting  too 


IRON.  129 

bulky    a    filtrate  for   the   subsequent   reduction.      Reserve   this 
solution. 

20.  Ignite  the  filter  and    residue  in  a  small  platinum  dish 
until  the  carbon  is  burned  off  and  then  cool  and   add  about  20 
drops  of  strong  sulphuric  acid  and  2  or  3  cc.  of  pure  strong  hydro- 
fluoric acid.      Digest  at  a  gentle  heat  very  cautiously  to  avoid 
spattering.      Finally  evaporate  to  sulphuric  acid  fumes  to  expel 
the  hydrofluoric  acid,  then  cool,  add  a  little  water  and  a  few  drops 
of  hydrochloric  acid    and  warm  if  necessary  to  effect  solution. 
If  this  treatment  proves  successful  the  liquid  in  the  dish  may  be 
added  to  the  main  solution  in  the    flask  without  filtering,  and 
the  reduction  and  subsequent  operations  proceeded  with  as  pre- 
viously described  (14). 

21.  If  the  mixture  of  sulphuric  and  hydrofluoric  acids  fails  to 
dissolve  the  residue,  proceed  as  follows :  Evaporate  to  white  fumes, 
add  about  0.5  gram  of  potassium  acid  sulphate,  and  heat  cautiously, 
to  avoid  spattering,  until  the  mass  is  in  quiet  fusion  and  the  specks 
of  iron  oxide  have  dissappeared.     After  cooling,  take  up  by  warm- 
ing with  a  little  water  and  a  few  drops  of  hydrochloric  acid. 
Proceed  with  the  solution  as  directed  above. 

22.  Titaniferous   Ores. — In  case  an  ore  contains  an  appre- 
ciable amount  of  titanic  acid  it  becomes  impracticable  to  use 
zinc  as  a  reducing  agent,  since  the  TiO2  in  solution  is  thereby 
reduced  to  T^Oa  (which  imparts  a  purple  or  blue  color  to  the 
liquid),  and  the  latter  is  subsequently  oxidized  back  to  TiO2 
again  by  the  permanganate.     Thus  more  permanganate  will  be 
required  than  corresponds  to  the  amount  of  iron  present. 

With  such  titaniferous  ores,  proceed  as  described  for  REFRAC- 
TORY OXIDES  (19)  until  the  final  solution  of  the  ore  and  residue  is 
obtained  in  the  flask  ready  for  reduction.  Now  drop  into  the 
flask  2  or  3  small  spirals  of  platinum  wire  to  prevent  subsequent 
bumping.  Boil  the  sokition,  if  necessary,  so  as  to  reduce  its 


130  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

bulk  to  about  40  cc.,  and  then  cautiously  add  enough  ammonia 
to  produce  a  slight  permanent  precipitate  of  ferric  hydroxide 
which  persists  even  after  vigorous  shaking.  Now  add  5  cc.  of 
a  strong  solution  of  ammonium  acid  sulphite,*  shake  well,  and 
then  warm  the  flask  gently.  As  the  deep-red  color  fades,  increase 
the  heat  gradually  to  the  boiling-point.  When  quite  colorless, 
add  a  mixture  of  10  cc.  of  strong  sulphuric  acid  and  20  cc.  of 
water  and  continue  the  boiling  until  all  odor  of  sulphur  dioxide' 
has  disappeared.  Now  place  the  flask  in  cold  water  and  add 
cold  water  until  the  flask  is  nearly  full.  When  the  solution  is 
quite  cold,  transfer  it  to  a  battery- jar,  dilute  to  700  cc.,  and  titrate 
with  permanganate  as  usual  (8). 

23.  Chrome-iron  Ore. — Treat  as  described  in  xn,  2.     After 
filtering  off  the  chromium  the  iron  is  left  with  the  residue  on  the 
filter  as  ferric  hydroxide.     With  as  little  hot  water  as  possible 
rinse  the  residue  from  the  filter  into  a  small  beaker.     Place  the 
latter  under  the  funnel  and  dissolve  whatever  precipitate  still 
adheres  to  the  filter  by  slowly  pouring  through  the  latter  a  warm 
mixture   of    10  cc.   strong   hydrochloric   acid   and    15  cc.    water. 
Heat  the  mixture  in  the  beaker  to  dissolve  all  the  ferric  hydroxide 
and  then  transfer  to  an  8-oz.  flask,  reduce  with  zinc,  and  deter- 
mine the  iron  according  to  14. 

24.  Zimmerman-Reinhardt    Method    as    Modified    by    Mixer 
and  Dubois.t — This  modification  of  the  permanganate   method 
is   extensively  used  in  the  Lake  Superior  region  for  the  rapid 
determination  of  iron  in  the  oxidized  ores  of  that  section. 

The  following  solutions  are  required : 


*  Ammonium  acid  sulphite  may  be  made  by  passing  sulphur  dioxide  into 
strong  ammonia  water  until  the  liquid  becomes  of  a  yellowish  color  and  smells 
strongly  of  sulphur  dioxide.  An  old  solution  always  contains  some  thiosulphate 
which  will  give  a  precipitate  of  sulphur  with  ferric  salts. 

t  Jour.  Am.  Chem.  Soc.,  XVII,  405. 


IRON.  131 

Stannous  Chloride.  Dissolve  i  pound  of  stannous  chloride 
in  i  pound  of  strong  hydrochloric  acid  (1.2  sp.  gr.)  to  which 
some  water  has  been  added  and  dilute  to  2  liters. 

Hydrochloric  Acid  of  i.i  Sp.  Gr.  Mix  equal  volumes  of  the 
strong  acid  (1.2  sp.  gr.)  and  water. 

Mercuric  Chloride.  Make  a  saturated  solution  in  hot  water, 
allow  to  cool  and  crystallize  and  then  filter. 

Manganese  Sulphate.  Dissolve  160  grams  in  water  and 
dilute  to  1750  cc.  To  this  add  330  cc.  of  phosphoric  acid  syrup 
of  1.7  sp.  gr.  and  320  cc.  of  sulphuric  acid,  1.84  sp.  gr.  This 
solution  is  to  obviate  the  deleterious  action  of  liberated  chlorine 
when  potassium  permanganate  is  added  to  a  hydrochloric  acid 
solution.  The  phosphoric  acid  allows  the  formation  of  iron 
phosphate,  which,  being  nearly  colorless,  renders  the  end-reaction 
more  distinct. 

25.  Treatment  of  an  Ore. — Treat  0.5  gram  in  a  small  covered 
beaker  with  2.5  cc.  of  the  stannous  chloride  solution  and  10  to  15 
cc.  of  the  dilute  hydrochloric  acid.  Boil  the  mixture  very  gently 
on  an  iron  plate  until  the  ore  is  completely  decomposed.  For 
ores  running  less  than  55  per  cent,  of  iron  it  is  advisable  to  use 
a  little  less  stannous  chloride.  The  solution  of  the  ore  is  usually 
very  rapid,  requiring  only  a  few  minutes. 

When  the  ore  is  dissolved,  run  a  few  drops  of  stannous  chloride 
from  a  burette  into  the  hot  solution  until  all  the  iron  is  reduced 
to  the  ferrous  state,  as  indicated  by  the  disappearance  of  the 
greenish-yellow  color.  If  an  excess  of  stannous  chloride  has 
been  originally  added,  it  is  of  course  unnecessary  to  add  more. 
In  any  case,  to  avoid  too  great  an  excess  of  stannous  chloride, 
which  is  undesirable,  it  is  advisable  to  add  a  few  drops  of  potassium 
permanganate  solution  to .  the  reduced  mixture  to  once  more 
slightly  oxidize  the  solution.  The  solution,  in  its  slightly  oxidized 
condition,  should  be  kept  warm  until  ready  to  titrate  and  then 


I32  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

the  final  reduction  made  with  a  drop  or  two  of  stannous  chloride, 
avoiding  unnecessary  excess.  Now  wash  down  the  sides  of  the 
beaker  and  add,  while  stirring,  5  cc.  of  the  mercuric  chloride 
solution  to  take  up  the  excess  of  stannous  chloride.  Have  ready 
a  5oo-cc.  beaker  containing  6-8  cc.  of  the  manganese  sulphate 
solution  and  about  400  cc.  of  cold  water.  Wash  the  iron  solution 
into  this  and  titrate  at  once  with  potassium  permanganate  in 
the  usual  way. 

Ores  containing  organic  matter,  some  magnetites,  and  pyritous 
ores  require  the  usual  precautions.  With  ores  containing  very 
large  amounts  of  organic  matter,  it  is  generally  most  advan- 
tageous to  burn  off  directly  and  follow  the  regular  method.  Ores 
containing  small  amounts  of  organic  matter  and  slightly  pyritous 
ores  are  dissolved  in  hydrochloric  acid  and  oxidized  with  potas- 
sium chlorate,  after  which  the  regular  method  is  pursued.  Heavy 
sulphides  may  be  treated  with  nitric  acid  as  described  in  31, 
and  the  hydrochloric  acid  solution  eventually  obtained  treated 
as  above.  Magnetites  should  be  ground  very  fine  in  an  agate 
mortar  and  then,  rf  unable  to  effect  complete  solution,  either  the 
ore  or  the  insoluble  residue  may  be  treated  as  described  in  21. 

26.  Bichromate  Method.* — The  following  solutions  are  re-/ 
quired : 

Stannous  Chloride.  This  should  be  strongly  acid  and  con- 
tain about  15  grams  of  tin  and  350  cc.  of  strong  hydrochloric 
acid  to  the  liter.  It  may  be  made  by  dissolving  the  tin  in  the 
acid  by  the  aid  of  heat  and  diluting.  It  is  usually  more  con- 
venient to  prepare  it  from  the  crystallized  stannous  chloride  as 
follows:  Dissolve  14.5  grams  of  the  crystals  in  165  cc.  of  strong 
hydrochloric  acid  and  dilute  to  500  cc.  Keep  in  a  half-liter 
bottle  in  which  a  stick  of  pure  tin  is  placed  to  prevent  oxidation. 

*  The  method  ordinarily  employed  for  ores  in  my  laboratory. 


IRON.         .  133 

One  cubic  centimeter  of  this  solution  will  reduce  about  0.015 
gram  of  iron  from  the  ferric  to  the  ferrous  condition.  It  will 
naturally  become  somewhat  stronger  as  the  stick  of  tin  gradually 
dissolves  in  the  acid  liquid. 

Mercuric  Chloride.  Use  a  saturated  solution  and  ke^p  an 
excess  of  the  crystals  in  the  bottle.  Such  a  solution  will  contain 
at  least  60  grams  of  mercuric  chloride  to  the  liter.  About  1.2  cc. 
of  this  solution  will  oxidize  the  tin  in  i  cc.  of  the  above  stannous 
chloride  solution,  at  its  original  strength,  to  the  stannic  condi- 
tion. 

Potassium  Ferricyanide.  This  solution  should  be  dilute,  say 
o.i  gram  in  15  cc.  of  water.  The  exact  strength  is  immaterial 
It  is  best  made  frequently,  or  when  required,  in  small  quantity, 
as  the  solution  does  not  keep  indefinitely. 

27.  Standard  Potassium  Bichromate.  —  This  should  contain 
4.39  grams  of  the  pure  salt  per  liter.     On  the  basis  of  0.5  gram 
of  ore  being  taken  for  assay,  i  cc.  of  a  solution  of  exactly  this 
strength  will  equal  i  per  cent,  of  iron.     This  is  shown  by  the 
equation 

6FeCl2  +  K2Cr2O7  +  I4HC1  -  6FeCl3  +  2KC1 + 2CrCl3  +  7H2O. 

Thus  i  molecule  of  potassium  dichromate  oxidizes  6  mole- 
cules of  ferrous  chloride  to  ferric  chloride,  or,  i  molecule  of 
K2Cr2O7  =  6Fe.  This  corresponds  to  294.5  parts  of  K2Cr2O7  to 
335.4  parts  of  Fe.  Hence  i  per  cent.,  or  0.005  grarn  of  iron  when 
0.5  gram  of  ore  is  taken  for  assay,  requires  0.00439  gram  of 
K2Cr2Oy.  If  this  amount  is  contained  in  i  cc.  then  the  liter 
will  contain  4.39  grams  of  K.2Cr2O7. 

28.  Standardize  the  dichromate  solution  as  follows:    Weigh 
carefully  0.15-0.20  gram  of  the  purest  iron  wire  obtainable  (see 
remarks  in  4  relative  to  the  iron  used  for  standardizing)  and 
dissolve  it  in  an  8-oz.  flask  in  a  mixture  of  5  cc.  each  of  strong 


134  TECHNICAL    METHODS  OF  ORE   ANALYSIS. 

nitric  and  hydrochloric  acids.  When  the  wire  has  dissolved  add 
5  cc.  of  strong  sulphuric  acid  and  boil  over  a  free  flame  (manip- 
ulating the  flask  in  a  holder)  until  the  hydrochloric  and  nitric 
acids  are  expelled  and  most  of  the  sulphuric  also.  Before  adding 
the  sulphuric  acid  see  that  all  salts  are  in  solution  (if  necessary 
adding  more  hydrochloric  acid),  otherwise  separated  nitrates  may 
not  be  completely  decomposed.  Allow  to  cool,  add  about  30  cc. 
of  water  and  5  cc.  of  strong  hydrochloric  acid  and  heat  the  mix- 
ture gently  until  solution  is  complete. 

29. (To  the  hot  solution  now  add  the  stannous  chloride  solu- 
tion cautiously  until  decolorization  is  complete,  avoiding  more 
than  a  slight  excess.  Transfer  the  reduced  solution  to  a  large 
beaker,  washing  out  the  flask  with  cold  water.  Add  about  10  cc. 
of  the  mercuric  chloride  solution,  pouring  it  in  rapidly  while 
stirring  the  mixture.  If  only  a  slight  excess  of  stannous  chloride 
was  used,  the  10  cc.  of  mercuric  chloride  will  be  ample  and  a 
white  precipitate  will  be  produced,  but  if  the  excess  of  stannous 
chloride  was  large  the  precipitate  may  become  gray  or  black 
from  the  separation  of  metallic  mercury.]  This  discoloration 
should  be  watched  for  carefully,  and  if  the  faintest  trace  of  it 
appears  add  an  abundance  of  the  mercuric  chloride  solution  at 
once.  If  this  restores  the  pure  white  color  the  test  may  proceed, 
otherwise  it  is  spoiled  and  must  be  begun  anew. 

The  reactions  involved  are,  first, 

2FeCl3  +  SnCl2  =  2FeCl2  +  SnCl4. 

The  stannous  chloride  thus  reduces  the  ferric  to  ferrous  chloride 
and  becomes  itself  oxidized  to  stannic  chloride.  The  excess  of 
stannous  chloride  added,  when  treated  with  sufficient  mercuric 
chloride,  is  oxidized  to  stannic  chloride  as  follows: 


Mercurous  chloride  is  produced,  which  is  a  white  precipitate. 
If  the  excess  of  stannous  chloride  is  large,  however,  so  that  the 


IRON.  135 

mercuric  chloride  added  is  insufficient  for  the  last  reaction,  trie 
following  takes  place: 

SnCl2 +HgCl2  =  SnCl4  -f  Hg. 

The  finely  divided  metallic  mercury  discolors  the  liquid.  If 
more  mercuric  chloride  be  added  at  once,  the  mercury  may  fre- 
quently be  taken  into  combination  again: 

Hg+HgCl2  =  Hg2Cl2. 


c 


The  liquid  therefore  contains  as  a  final  result,  ferrous  cnloride, 
stannic  chloride,  mercuric  chloride,  and  a  precipitate  of  white 
mercurous  chloride.  The  only  one  of  these  compounds  affected  by 
the  dichromate  in  the  subsequent  titration  is  the  ferrous  chlorideJ 

30.  The  mixture  in  the  beaker  is  now  ready  for  the  titra- 
tion, which  should  be  proceeded  with  without  delay,  since  after 
the  mercuric  chloride  has  been  added  there  is  nothing  to  prevent 
oxidation  of  the  ferrous  solution.  Have  ready  a  glazed  porcelain 
tile  either  with  or  without  depressions,  a  beaker  or  glass  full  of 
water  in  which  is  placed  a  glass  rod,  and  also  the  test  solution 
of  potassium  ferricyanide.  Run  in  the  dichromate  solution  from 
the  burette  while  stirring  the  iron  solution,  and  from  time  to  time 
place  a  drop  of  the  latter  on  the  porcelain  and  touch  it  with  a 
drop  of  the  ferricyanide.  For  the  latter  purpose  use  the  rod 
placed  in  the  glass  of  water,  and  after  each  test  return  it  to  the 
glass  and  it  will  thus  be  kept  sufficiently  washed.  As  long  as  a 
large  amount  of  iron  still  remains  in  the  ferrous  condition  the 
ferricyanide  will  produce  intensely  blue  tests,  and,  in  order  not 
to  be  deceived  in  the  matter,  endeavor  to  add  a  sufficiently  large 
drop  of  the  ferricyanide  each  time  to  combine  and  produce  a 
blue  color  with  all  the  ferrous  chloride  present  in  the  test  drop. 
Continue  to  thus  run  in  the  dichromate  solution  until  the  color 
of  the  tests  becomes  fainter.  Proceed  then  with  more  caution, 


136  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

finally  drop  by  drop,  until  a  test  is  obtained  that  fails  to 
a  blue  tint  after  waiting  half  a  minute.  In  making  the  final  tests 
use  less  and  less  of  the  ferricyanide,  as  the  delicacy  of  the  reaction 
depends  upon  having  just  about  enough  ferricyanide  present 
to  combine  with  the  ferrous  chloride  still  remaining,  an  excess 
producing  an  abnormal  color  that  obscures  the  true  end-point. 
Finally  read  the  number  of  cubic  centimeters  used,  and,  from 
the  weight  of  iron  taken,  calculate  the  value  of  i  cc.  in  iron. 

Example. — Suppose  0.17  gram  of  iron  wire,  actually  contain- 
ing 0.1697  gram  of  iron,  were  taken,  and  that  33.8  cc.  of  dichro- 
mate  solution  were  used-  Then  the  value  of  i  cc.  is  0.1697  •*• 
33.8,  or  0.005021  gram  of  iron. 

When  0.5  gram  of  ore  is  taken  for  assay,  i  cc.  of  the  dichro- 
mate  solution  will  equal  1.004  per  cent,  of  iron. 

31.  Treatment  of  an  Ore. — Take  0.5  gram  of  the  ore.  The 
method  of  decomposition  will  depend  upon  the  nature  of  the 
sample.  Whenever  possible  hydrochloric  acid  alone  should 
be  used.  When  the  sample  appears  to  be  more  or  less  of  an 
oxidized  nature  always  try  hydrochloric  acid  first,  using  10  cc. 
and  warming  the  mixture  in  an  8-oz.  flask.  Take  all  the  time 
and  acid  necessary,  but  do  not  boil  violently,  as  this  weakens 
the  acid  and  fails  to  effect  as  rapid  a  solution  as  a  gentler  heat. 
If  undecomposed  sulphides  remain,  add  1-2  cc.  of  strong  nitric 
acid  and  continue  the  heating.  The  final  insoluble  residue 
should  be  clean  and  white.  If  hydrochloric  acid  alone  effects 
a  complete  decomposition,  boil  the  solution  finally  to  pastiness, 
add  about  30  cc.  of  water  and  then  5  cc.  of  strong  hydrochloric 
acid.  These  last  operations  are  simply  to  insure  about  the  proper 
proportion  of  acid  present  for  the  succeeding  steps.  If  nitric 
acid  has  been  used  in  the  decomposition,  first  see  that  all  soluble 
matter  is  still  held  in  solution  (otherwise  adding  more  hydro- 
chloric acid),  then  add  5  cc.  of  strong  sulphuric  acid  and  boil, 


IRON.  137 

best  over  a  free  flame,  as  nearly  as  possible  to  dryness,  so  as  to 
expel  most  of  the  sulphuric  acid.  It  is  very  difficult,  if  not 
impossible,  to  completely  decompose  solid  nitrates,  that  have 
separated  from  the  solution  by  concentration,  by  boiling  with 
sulphuric  acid.  After  cooling,  add  about  75  cc.  of  water  and 
5  cc.  of  strong  hydrochloric  acid.  It  is  unnecessary  to  heat  the 
mixture  to  effect  solution  of  the  salts  at  this  stage. 

Observe  that  whatever  method  of  decomposition  is  employed 
there  is  finally  obtained  a  solution  or  mixture  containing  about 
5  cc.  of  free  hydrochloric  acid. 

32.  To  the  mixture  in  the  flask  add  about  0.2  gram  of  pure 
cupric  sulphate  and  see  that  it  dissolves,  or  better,  an  equivalent 
amount  of  strong  solution.  Now  add  about  20  grams  of  pure, 
finely  granulated  test-lead,  and  boil  gently  to  effect  the  reduction 
of  the  iron  to  the  ferrous  condition.  The  copper  precipitates 
on  the  lead  and  prevents  it  from  cohering  in  lumps.  If  the  ore 
already  contains  sufficient  copper  it  is  of  course  unnecessary  to 
add  more.  Avoid  adding  the  lead  to  a  boiling-hot  solution  or 
it  will  probably  produce  a  sudden  evolution  of  steam  and  over- 
flow the  flask.  The  iron  is  usually  entirely  reduced  by  about 
five  minutes'  gentle  boiling.  It  is  best  to  boil  for  a  few  minutes 
after  the  liquid  has  become  completely  decolorized.  The  copper 
is  thus  all  precipitated  and  any  arsenic  or  antimony  also  removed 
from  the  solution.  Prolonged  boiling  causes  the  formation  of 
too  much  lead  chloride,  which  separates  out  and  renders  the 
solution  difficult  to  filter.  Filter  boiling-hot,  bringing  the  excess 
of  lead  upon  the  filter,  and  wash  thoroughly  with  hot  water. 
Receive  the  filtrate  in  a  large  beaker  in  which  5  cc.  of  strong 
hydrochloric  acid  and  2  cc.  of  the  prepared  stannous  chloride 
solution  (26)  have  previously  been  placed.  The  acid  is  simply 
to  insure  sufficient  acidity  and  the  stannous  chloride  is  to  reduce 
any  ferric  chloride  that  may  possibly  be  present  and  keep  it 


138  TECHNICAL   METHODS  OF  ORE   ANALYSIS. 

reduced.  Stir  the  mixture  in  the  beaker  after  nitration.  As  it 
contains  a  little  stannous  chloride  the  ferrous  chloride  will  not 
become  oxidized  by  standing  a  short  time  at  this  stage. 

33.  The  burette   and   other  arrangements   being    ready  (as 
described  in  30),  add  10  cc.  or  mercuric  chloride  solution  (26) 
to  the  liquid  in  the  beaker  and  titrate  as  described  for  the  stand- 
ardization of  the  dichromate  solution  (30).      From  the  number 
of  cubic  centimeters  of  dichromate  solution  used  and   the  known 
value  in  iron  of  i  cc.,  calculate  the  percentage  of  iron  in  the  ore. 

34.  Silicates,  Refractory  Oxides,  etc. — Decompose  these  sub- 
stances as  described  either  in  17,  18,  19   or  23,  so  as  to  finally 
obtain    the  iron  in  hydrochloric  acid  solution  containing  about 
5  cc.  of  the  strong  acid.     Proceed  with  this  solution  as  described 
in  32. 

35.  Standard  Methods  for  the  Analysis  of  Iron.*— 

Determination  of  Silicon. 

Weigh  i  gram  of  sample,  add  30  cc.  nitric  acid  (sp.gr.  1.13); 
then  5  cc.  sulphuric  acid  (cone.).  Evaporate  on  hot  plate  until 
all  fumes  are  driven  off.  Take  up  in  water  and  boil  until  all 
ferric  sulphate  is  dissolved.  Filter  on  an  ashless  filter,  with  or 
without  suction  pump,  using  a  cone.  Wash  once  with  hot  water, 
once  with  hydrochloric  acid,  and  three  or  four  times  with  hot 
water.  Ignite,  weigh,  and  evaporate  with  a  few  drops  of  sul- 
phuric acid  and  4  or  5  cc.  of  hydrofluoric  acid.  Ignite  slowly 
and  weigh.  Multiply  the  difference  in  weight  by  .4702,  which 
equals  the  per  cent,  of  silicon. 

*  1907  Report  of  the  Committee  of  the  American  Foundrymen's  Association. 


IRON.  I39 

Determination  of  Sulphur. 

Dissolve  slowly  a  3-gram  sample  cf  drillings  in  concen- 
trated nitric  acid  in  a  platinum  dish  covered  with  an  inverted 
watch  glass.  After  the  iron  is  completely  dissolved,  add  2 
grams  of  potassium  nitrate,  evaporate  to  dryness  and  ignite  over 
an  alcohol  lamp  at  red  heat.  Add  50  cc.  of  a  i  per  cent,  solu- 
tion of  sodium  carbonate,  boil  for  a  few  minutes,  filter,  using  a 
little  paper  pulp  in  the  filter  if  desired,  and  wash  with  a  hot 
i  per  cent,  sodium  carbonate  solution.  Acidify  the  filtrate  with 
hydrochloric  acid,  evaporate  to  dryness,  take  up  with  50  cc.,  of 
water  and  2  cc.  of  concentrated  hydrochloric  acid,  filter,  wash, 
and  after  diluting  the  filtrate  to  about  100  cc.,  boil  and  precipitate 
with  barium  chloride.  Filter,  wash  well  with  hot  water,  ignite 
and  weigh  as  barium  sulphate,  which  contains  13.733  Per  cenk 
of  sulphur. 

Determination  of  Phosphorus. 

Dissolve  2  grams  sample  in  50  cc.  nitric  acid  (sp.  gr.  1.13), 
add  10  cc.  hydrochloric  acid  and  evaporate  to  dryness.  In  case 
the  sample  contains  a  fairly  high  percentage  of  phosphorus  it 
is  better  to  use  half  the  above  quantities.  Bake  until  free  from 
acid,  redissolving  in  25  to  30  cc.  of  concentrated  hydrochloric 
acid,  dilute  to  about  60  cc.,  filter  and  wash.  Evaporate  to  about 
25  cc.,  add  20  cc.  concentrated  nitric  acid,  evaporate  until  a  film 
begins  to  form,  add  30  cc.  of  nitric  acid  (sp.  gr.  1.20)  and  again 
evaporate  until  a  film  begins  to  form.  Dilute  to  about  150  cc. 
with  hot  water  and  allow  it  to  cool.  When  the  solution  is  be- 
tween 70°  and  80°  C.,  add  50  cc.  of  molybdate  solution.  Agitate 
the- solution  a  few  minutes,  then  filter  on  a  tared  Gooch  crucible 
having  a  paper  disc  at  the  bottom.  Wash  three  times  with  a 
3  per  cent,  nitric  acid  solution  and  twice  with  alcohol.  Dry 


140  TECHNICAL  METHODS  OF  ORE  ANALYSIS, 

at  100°  to  105°  C.,  to  constant  weight.  The  weight  multiplied 
by  0.0163  ecluals  the  per  cent,  of  phosphorus  in  a  i  gram,  sample. 
To  make  the  molybdate  solution  add  100  grams  molybdic 
acid  to  250  cc.  water,  and  to  this  add  150  cc.  ammonia,  then  stir 
until  all  is  dissolved  and  add  65  cc.  nitric  acid  (sp.  gr.  1.42). 
Make  another  solution  by  adding  400  cc.  concentrated  nitric 
acid  to  1,100  cc.  water,  and  when  the  solutions  are  cool,  pour  the 
first  slowly  into  the  second  with  constant  stirring  and  add  a 
couple  of  drops  of  ammonium  phosphate. 

Determination  of  Manganese. 

Dissolve  1. 10  grams  of  drillings  in  25  cc.  nitric  acid  (sp.  gr. 
1.13),  filter  into  an  Erlenmeyer  flask  and  wash  with  30  cc. 
of  the  same  acid.  Then  cool  and  add  about  0.5  gram  of 
sodium  bismuthate  until  a  permanent  pink  color  forms.  Heat 
until  the  color  has  disappeared,  with  or  without  the  precipitation 
of  manganese  dioxide,  and  then  add  either  sulphurous  acid  or  a 
solution  of  ferrous  sulphate  until  the  solution  is  clear.  Heat  untii 
all  nitrous  oxide  fumes  have  been  driven  off,  cool  to  about  15°  C.; 
add  an  excess  of  sodium  bismuthate  —  about  i  gram  —  and 
agitate  for  two  or  three  minutes.  Add  50  cc.  water  containing 
30  cc.  nitric  acid  to  the  liter,  filter  on  an  asbestos  filter  into  an 
Erlenmeyer  flask,  and  wash  with  50  to  100  cc.  of  the  nitric  acid 
solution.  Run  in  an  excess  of  ferrous  sulphate  and  titrate  back 
with  potassium  permanganate  solution  of  equal  strength.  Each 
cubic  centimeter  of  N/io  ferrous  sulphate  used  is  equal  to  o.io 
per  cent,  of  manganese. 

Determination  of  Total  Carbon. 

This  determination  requires  considerable  apparatus;  so  in 
view  of  putting  as  many  obstacles  out  of  the  way  of  its  general 
adoption,  in  cases  of  dispute  your  committee  has  left  optional 


IRON.  141 

several  points  which  were  felt  to  bring  no  chance  of  error  into  the 
method. 

The  train  shall  consist  of  a  pre-heating  furnace,  containing 
copper  oxide  (Option  No.  i )  followed  by  caustic  potash  (sp.  gr. 
i. 20),  then  calcium  chloride,  following  which  shall  be  the 
combustion  furnace  in  which  either  a  porcelain  or  platinum  tube 
may  be  used  (Option  No.  2).  The  tube  shall  contain  4  or 
5  inches  of  copper  oxide  between  plugs  of  platinum  gauze,  the 
plug  to  the  rear  of  the  tube  to  be  at  about  the  point  where  the 
tube  extends  from  the  furnace.  A  roll  of  silver  foil  about  2 
inches  long  shall  be  placed  in  the  tube  after  the  last  plug  of 
platinum  gauze.  The  train  after  the  combustion  tube  shall  be 
anhydrous  cupric  sulphate,  anhydrous  cuprous  chloride,  calcium 
chloride,  and  the  absorption  bulb  of  potassium  hydrate  (sp.  gr. 
1.27)  with  prolong  filled  with  calcium  chloride.  A  calcium 
chloride  tube  attached  to  the  aspirator  bottle  shall  be  connected 
to  the  prolong. 

In  this  method  a  single  potash  bulb  shall  be  used,  a  second 
bulb  as  sometimes  used  for  a  counterpoise  being  more  liable  to 
introduce  error  than  correct  error  in  weight  of  the  bulb  in  use, 
due  to  change  of  temperature  or  moisture  in  the  atmosphere. 

The  operation  shall  be  as  follows:  To  i  gram  of  well  mixed 
drillings  add  100  cc.  of  potassium  copper  chloride  solution  and 
7.5  cc.  of  hydrochloric  acid  (cone.).  As  soon  as  dissolved,  as 
shown  by  the  disappearance  of  all  copper,  filter  on  previously 
washed  and  ignited  asbestos.  Wash  thoroughly  the  beaker  in 
which  the  solution  was  made  with  20  cc.  of  dilute  hydrochloric 
acid  (i  :  i),  pour  this  on  the  filter  and  wash  the  carbon  out  of  the 
beaker  by  means  of  a  wash  bottle  containing  dilute  hydrochloric 
acid  (i  :  i)  and  then  wash  with  warm  water  until  all  the  acid  is 
washed  out  of  the  filter.  Dry  the  carbon  at  a  temperature 
between  95°  and  100°  C. 


142  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

Before  using  the  apparatus  a  blank  shall  be  run  and  if  the  bulb 
does  not  gain  in  weight  more  than  0.5  milligram,  put  the  dried 
filter  into  the  ignition  tube  and  heat  the  pre-heating  furnace  and 
the  part  of  the  combustion  furnace  containing  the  copper  oxide. 
After  this  is  heated  start  the  aspiration  of  oxygen  or  air  at  the  rate 
of  3  bubbles  per  second,  to  show  in  the  potash  bulb.  Continue 
slowly  heating  the  combustion  tube  by  turning  on  two  burners  at 
a  time,  and  continue  the  combustion  for  30  minutes  if  air  is 
used;  20  minutes  if  oxygen  is  used.  (The  Shinier  crucible  is 
to  be  heated  with  a  blast  lamp  for  the  same  length  of  time. ) 

When  the  ignition  is  finished  turn  off  the  gas  supply  gradually 
so  as  to  allow  the  combustion  tube  to  cool  off  slowly  and  then 
shut  off  the  oxygen  supply  and  aspirate  with  air  for  10  minutes. 
Detach  the  potash  bulb  and  prolong,  close  the  ends  with  rubber 
caps  and  allow  it  to  stand  for  5  minutes,  then  weigh.  The 
increase  in  weight  multiplied  by  0.27273  equals  the  percentage 
of  carbon. 

The  potassium  copper  chloride  shall  be  made  by  dissolving 
i  pound  of  the  salt  in  i  liter  of  water  and  filtering  through  an 
asbestos  filter. 

Option  No.  i.  —  While  a  pre-heater  is  greatly  to  be  desired, 
as  only  a  small  percentage  of  laboratories  at  present  use  them 
it  was  decided  not  to  make  the  use  of  one  essential  to  this  method; 
subtraction  of  the  weight  of  the  blank  to  a  great  extent  eliminating 
any  error  which  might  arise  from  not  using  a  pre-heater. 

Option  No.  2.  —  The  Shinier  and  similar  crucibles  are  largely 
used  as  combustion  furnaces,  and  for  this  reason  it  was  decided 
to  make  optional  the  use  of  either  the  tube  furnace  or  one  of  the 
standard  crucibles.  In  case  the  crucible  is  used  it  shall  be 
followed  by  a  copper  tube  3/16  inch  inside  diameter  and  10 
inches  long,  with  its  ends  cooled  by  water  jackets.  In  the  center 
of  the  tube  shall  be  placed  a  disk  of  platinum  gauze,  and  for 


IRON.  143 

3  or  4  inches  in  the  side  towards  the  crucible  shall  be  silver  foil 
and  for  the  same  distance  on  the  other  side  shall  be  copper 
oxide.  The  ends  shall  be  plugged  with  glass  wool,  and  the  tube 
heated  with  a  fish  tail  burner  before  the  aspiration  of  air  is  started. 

Graphite. 

Dissolve  i  gram  of  sample  in  35  cc.  of  nitric  acid  (sp.  gr.  1.13), 
filter  on  asbestos,  wash  with  hot  water,  then  with  potassium 
hydrate  (sp.  gr.  i.i),  and  finally  with  hot  water.  The  graphite 
is  then  ignited  as  specified  in  the  determination  of  total  carbon. 


CHAPTER  XVI. 
LEAD. 

MANY  methods  have  been  proposed  for  the  technical  deter- 
mination of  lead  in  ores,  etc.  The  following  method,  which 
is  the  result  of  much  patient  experiment,  is  in  daily  use  in 
my  laboratory.  I  find  it  more  generally  satisfactory  than  any 
other. 

1.  Chr ornate  Method. — Prepare  the  following  solutions: 
Extraction  Solution.     Make  a  cold  saturated  solution  of  com- 
mercial sodium  acetate  in  distilled  water  and  filter  it.     Mix  i 
volume  with  two  volumes  of  distilled  water  and  add  to  the  mix- 
ture 30  cc.  of  80  per  cent,  acetic  acid  per  liter.     Used  nearly 
boiling  in  a  wash-bottle. 

Hydrochloric  Acid  Mixture.  Make  a  cold  saturated  solution 
of  table  salt  in  distilled  water  and  filter  it.  To  i  liter  of  the 
filtrate  add  150  cc.  of  distilled  water  and  100  cc.  of  strong  hydro- 
chloric acid.  Used  cold  in  a  wash-bottle. 

Potassium  Dichromate.  A  cold  saturated  solution  of  the 
powdered  commercial  salt  in  distilled  water.  Filter,  or  allow 
to  settle. 

Starch  Solution.     See  xin,  2. 

2.  Treatment  of  an  Ore.-^Weigh  0.5  gram  of  the  ore  into 
an  8-oz.  flask.     It  is  usually  best  to*  begin  the  treatment  with 
20  cc.  of  strong  hydrochloric  acid  and  heat  gently  until  all  iron 
oxide,  etc.,  is  in  solution.     This  will  also  decompose  galena  and 
expel   the  hydrogen  sulphide.)  If  sulphides  remain  that  resist 

H4 


LEAD.  145 

f  '-v 

hydrochloric  acid,  add  5  cc.  of  strong  nitric  acid  and  continue 
the  heating.  Finally,  if  necessary,  add  5-10  cc.  more  hydro- 
chloric acid  and  again  heat,  to  bring  all  the  lead  chloride  into 
solution. 

3  (^Decomposition  and  solution  having  been  satisfactorily 
effected,  add  5  cc.  of  strong  sulphuric  acid  and  boil,  finally,  over 
a  free  flame,  until  the  white  fumes  are  coming  off  copiously. 
Cool,  add  about  30  cc.  of  water  and  heat  to  boiling.  Allow  to 
stand,  hot,  until  the  anhydrous  ferric  sulphate  usually  present 
has  dissolved.  Now  add  10  cc.  of  alcohol  (either  grain~or-weed) 
and  then  cool  to  room  temperature,  or  cooler,  and  filter  through 
a  9-cm.  filter.  (The  alcohol  is  not  absolutely  essential  except 
for  the  low  percentages,  say  below  ten  per  cent,  lead.)  Wash 
the  precipitate  with  cold  dilute  (i-io)  sulphuric  acid  at  least 
-f  our  times. 

4.  Now  open  the  filter  carefully  and  spread  it  in  the  funnel. 
Wash  the  precipitate  from  it  into  the  flask  again  with  a  jet  of  hot 
water,  using  as  little  as  possible?)  Wash  every  trace  of  residue 
from  the  filter  with  the  extraction  solution,  nearly  boiling.  Add 
sufficient  additional  hot  extraction  solution  to  the  mixture  in 
the  flask  to  complete  the  solution  of  all  the  lead  sulphate.  If 
apparently  necessary,  which  is  seldom,  heat  to  boiling  and  filter, 
washing  with  extraction  solution.  Dilute  the  solution,  or  the 
filtrate,  to  150  cc.  with  hot  water.  It  is  best  to  have  a  similar 
flask,  with  a  mark  on  it  for  comparison,  so  as  to  always  obtain, 
approximately,  the  right  volume.  Heat  the  mixture  to  boiling 
and  see  that  all  lead  sulphate  is  in  solution.  The  amount  of  gangue 
in  the  unfiltered  mixture  is  usually  small  and  of  no  consequence. 
To  the  boiling  solution  ado1?  with  a  pipette,  10  cc.  of  tbis  prepared 
potassium  dichromate  solution.  Boil  the  mixture  very  gently  fot 
seven  minutes.  About  this  length  of  time  is  necessary  to  insure 


146  TECHNICAL   METHODS   OF   ORE   ANALYSIS. 

always  the  same  constitution  of  the  lead  chromate;  somewhat 
longer  does  no  harm.  Now  filter  through  an  n-cm.  filter.  Wash 
out  the  flask  with  hot  water  and  then  wash  the  filter  and  pre- 
cipitate ten  times  with  a  hot  dilute  solution  of  sodium  acetate 
(50  cc.  of  a  cold  saturated  solution  of  the  commercial  salt  diluted 
to  i  liter),  using  about  5-6  cc.  each  time.  Now  again  place  the 
clean  flask  under  the  funnel,  and,  with  a  jet  of  the  cold  hydro- 
chloric acid  mixture,  stir  up  and  dissolve  the  precipitate  on  the 
filter  and  continue  washing  with  the  same  mixture  until  all  the 

residue  and  every  trace  of  color  are  removed  from  the  filter.! 

/" — 

Use  at  least  50  cc.  of  the  mixture  in  any  case,  in  order  that  the 

subsequent  reactions  may  have  the  proper  conditions.  Wash  the 
filter  finally  with  cold  water,  or  at  once  dilute  the  filtrate  until 
the  flask  is  half  full.  Either  one  of  two  procedures  is  now  to  be 
followed,  according  to  the  amount  of  lead  apparently  present. 

5.  With  not  over  twenty  per  cent.  lead.  (  Add  2  cc.  of  a  fifty  per 
cent,  solution  of  potassium  iodide,  mix  and  titrate  at  once)  (to  v 
avoid  possible  loss  of  iodine  by  volatilization)  with  a  standard 
sodium  thiosulphate  solution  until  the  brown  color  becomes  faint; 
then  add  sufficient  starch  solution  to  produce  a  strong  blue  color 
and  finish  the  titratiori  very  slowly,  finally  drop  by  drop,  until 
the  solution  becomes  a  clear  pale  green  with  no  tinge  of  blue. 
The  end-point  is  very  sharp  and  care  must  be  exercised  or  it 
may  easily  be  passed.     It  is  best  to  have  a  white  surface  under 
the  flask. 

6.  With  over  twenty  per  cent.  lead.     Pour  all  but  about  25  cc. 
of  the  liquid  in  the  flask  into  a  beaker.     To  the  solution  still 
remaining,  add  about  25  cc.  of  the  hydrochloric  acid  mixture  and 
2  cc.  of  the  above  potassium  iodide  solution.    Mix  and  titrate 
at  once  with  the  standard  thiosulphate  until  the  brown  color  has 
become  faint.     Now  add  a  portion  of  the  solution  reserved  in 
the  beaker  and  again  titrate  to  a  faint  brown  color.    Continue 


LEAD.  147 

thus  until  the  last  of  the  reserved  solution  has  been  rinsed  into 
the  flask;  then  finish  the  titration  as  in  5.  In  pouring  from  the 
beaker  it  is  best  to  use  a  glass  rod,  so  as  to  avoid  having  to  wash 
the  lip  each  time  and  unnecessarily  increasing  the  volume  of 
liquid  in  the  flask,  otherwise  the  latter  may  become  inconve- 
niently full. 

7.  Standardize  the  thiosulphate  solution  on  pure  lead.  The 
thiosulphate  solution  used  in  the  iodide  copper  method  and  con- 
taining about  19.5  grams  of  the  crystallized  salt  per  liter  is  satis- 
factory for  lead.  Dissolve  about  0.2  gram  of  pure  lead  foil  in 
a  little  i :  2  nitric  acid  contained  in  an  8-oz.  flask,  and  boil  the 
solution  to  complete  dryness.  Cool,  add  about  30  cc.  of  water, 
then  5  cc.  of  strong  sulphuric  acid.  Boil  the  mixture  a  short 
time,  add  a  little  water  to  replace  that  lost  by  boiling,  then  10 
cc.  of  alcohol,  and  cool  to  room  temperature  or  cooler.  Filter 
the  lead  sulphate  and  continue  as  described  for  ores  (4).  Titrate 
as  described  in  6. 

One  cubic  centimeter  of  the  thiosulphate  will  be  found  to 
equal  a  little  more  than  0.005  gram  of  lead,  or  something  over 
one  per  cent,  on  the  basis  of  0.5  gram  of  ore  taken  for  assay 
The  copper  value  of  the  thiosulphate,  multiplied  by  1.078,  will 
give  a  close  approximation  to  the  lead  value. 

Notes.  The  final  solution  is  not  a  very  good  solvent  for 
iodine,  and  therefore,  if  much  is  liberated  at  once,  there  is  danger 
of  loss  by  volatilization.  To  avoid  this,  the  procedure  described 
in  6  for  the  higher  percentages  of  lead  has  been  found  the  best. 

The  amount  of  potassium  iodide  prescribed  is  much  more 
than  theoretically  required  in  any  case,  but  it  is  unsafe  to  ever 
use  less,  as  the  reactions  are  then  liable  to  proceed  too  slowly. 

Testing  the  completness  of  the  extraction  is  rarely  necessary, 
as  the  solution  of  all  the  lead  sulphate  is  usually  easily  seen. 

Prepare  only  a  wash-bottleful  of  the  dilute  sodium  acetate 


1 48  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

wash  at  a  time,  as,  unless  the  solution  is  heated  frequently,  a 
fungus  growth  develops  that  will  clog  the  filter. 

If  the  end-point  be  passed  in  titrating,  it.  may  be  "brought 
back"  with  a  dilute  solution  of  potassium  dichromate  or  per- 
manganate, of  which  the  comparative  value  need  not  be  known. 
Simply  run  in  from  a  burette  a  measured  number  of  drops  until 
the  blue  color  returns;  titrate  once  more  and  take  reading.  Now 
again  run  in  the  same  number  of  drops  of  the  correction  solution 
as  before  and  again  finish  the  thiosulphate  titration  and  read  the 
burette.  Subtract  the  difference  between  the  two  readings  from 
the  first  one  to  obtain  the  true  end-point  for  the  lead. 

If,  in  titrating  by  portions,  as  in  6,  the  end-point  be  slightly 
passed  with  any  of  the  portions,  no  appreciable  error  will  be 
introduced  if  more  of  the  reserved  solution  be  quickly  added,  as 
the  thiosulphate  solution  is  decomposed  only  very  slowly  by  the 
acid  mixture. 

The  constitution  of  the  lead  chromate  is  a  vital  point.  It 
depends  upon  the  various  conditions  of  heat,  acidity,  etc.  By 
operating  as  described,  differences  in  constitution  are  minimized 
and  a  slightly  acid  chromate  of  practically  constant  composition 
is  obtained.  The  normal  chromate,  under  the  conditions  obtain- 
ing, is  difficult  to  maitain  as  such. 

Bismuth  in  small  amount  does  not  interfere.  With  several  per 
cent,  present,  some  may  remain  as  basic  sulphate  with  the  lead 
sulphate  and  produce  high  results.  If  bismuth  is  suspected  it 
may  be  removed  just  before  filtering  the  lead  chromate  by  adding 
about  2  grams  of  citric  acid  dissolved  in  a  little  hot  water.  Any 
bismuth  chromate  will  go  into  solution  at  once.  Filter  without 
delay. 

8.  Ores  Containing  Barium. — When  a  lead  ore  contains 
barium  it  is  frequently  very  difficult  to  extract  the  lead  com- 
pletely from  the  mixed  sulphates  by  the  usual  procedure.  In 


LEAD.  149 

such  a  case,  either  before  or  after  attempting  the  usual  extrac- 
tion, drop  the  filter  and  residue  into  an  8-oz.  flask,  add  5-10  cc. 
of  strong  hydrochloric  acid  and  boil  to  pastiness,  almost  to  dry- 
ness,  the  filter  being  converted  into  a  pulp.  Avoid  going  so  far 
as  to  burn  the  filter  or  dry  it  on  to  the  flask.  Now  add  about 
25  cc.  of  the  usual  acetate  solution  (or  the  acetate  filtrate),  boil 
and  filter.  Wash  thoroughly,  first  with  the  hot  acetate  solution, 
then  with  hot  water.  Proceed  with  the  filtrate  in  the  usual 
manner. 

9.  Alexander's   Method,   Modified. — Alexander's   method,   or 
or  some  modification  of  it,  is  the  one  most  commonly  employed 
in  western  smelting  works.     The  principal  objections  to  it  that 
I  have  noted  are  the  difficulty  of  accurately  determining  very 
low  percentages  of  lead,  on  account  of  the  slowness  of  the  reac- 
tions in  such  cases,  and  the  occasional  failure  to  obtain  checking 
results  or  satisfactory  end-points  with  the  higher  percentages, 
for  no  apparent  reason.     The  following  modification  was  long 
used  in  my  laboratory: 

Treat  0.5  gram  of  the  ore  precisely  as  described  in  2  and  3 
and  extract  the  lead  sulphate  as  described  in  4.  (If  it  is  desired 
to  test  the  completness  of  the  extraction,  use  hydrogen  sulphide 
water,  instead  of  potassium  dichromate,  and  subsequently  add 
any  tested  washings  showing  lead  to  the  main  filtrate.  If  ammo- 
nium sulphide  is  used  for  testing,  a  discoloration  might  be 
obtained  that  was  due  to  iron,  which  is  frequently  present  in 
this  filtrate.)  Add  to  the  filtrate  in  the  flask  an  excess  of  ammo- 
nium sulphide.  It  is  a  good  plan,  although  not  essential,  to 
first  add  a  little  ammonia  to  neutralize  the  acid  and  prevent 
separation  of  sulphur.  Boil  for  a  moment  to  coagulate  the  lead 
sulphide  and  then  filter  and  wash  with  hot  water.  These  oper- 
ations entirely  remove  any  calcium  sulphate. 

10.  The  lead  sulphide  is  still  almost  certain  to  contain  a 


150  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

little  iron.  This  iron  is  originally  retained  by  the  lead  sulphate. 
If  allowed  to  remain  it  tends  to  obscure  the  end- point  of  the 
subsequent  titration  by  producing  a  color  with  the  tannic  acid 
used  for  testing.  It  is  best,  therefore,  to  remove  any  possible 
iron  in  every  case  as  follows:  Pour  through  the  precipitate  on 
the  filter  a  mixture  of  5  cc.  of  the  dilute  (1:10)  sulphuric  acid 
and  15  cc.  of  strong  hydrogen  sulphide  water,  and  then  wash 
with  cold  water. 

11.  Now  drop  filter  and  contents  into  the  flask  and  add  5  cc. 
of  strong  hydrochloric  acid.     Boil  the  mixture,  best  by  manipu- 
lating the  flask  over  a  small  free  flame  to  prevent  bumping,  to 
convert  the  lead  to  chloride  and  expel  hydrogen  sulphide,  the 
filter  meanwhile  becoming  well  disintegrated.     If  5  cc.  of  acid 
prove  insufficient  to  entirely  decompose  the  lead  sulphide,  add 
a  little  more,  but  avoid  using  a  large  excess.     In  any  case  boil 
off  half  or  more  of  the  acid  and  then,  to  the  hot  mixture,  add 
2-3  drops  of  strong  nitric  acid  to  oxidize  any  unexpelled  hydrogen 
sulphide.     Now  add  25  cc.  of  cold  water,  then  a  few  drops  of 
litmus  solution  as  an  indicator,  and  then  cautiously  add  ammonia 
in  very  slight  excess.   Finally,  make  distinctly  acid  with  acetic  acid. 

12.  Heat  the  mixture  in  the  flask  to  boiling,  dilute  to  about 
200  cc.  with  boiling- hot  water,  and  titrate  with  the  standard 
ammonium   molybdate   solution   as   follows:   Pour   about   two- 
thirds  of  the  hot  lead  solution  into  a  large  beaker  and  run  the 
molybdate  solution  into  it  from  a  burette  until  a  drop  from  the 
beaker,  when  placed  on  a  glazed  porcelain  plate  and  touched 
with  a  drop  of  a  solution  of  tannic  acid  (about  o.i  gram  dissolved 
in  20  cc.  of  water),  gives  a  brown  or  yellow  tinge.     Now  add 
more  of  the  lead  solution  from  the  flask  and  continue  the  titration 
until  the  end- point  is  again  passed-     Continue  thus  to  approach 
the  true  end-point,  using  more  caution  each  time.     Finally,  when 
only  a  few  cubic  centimeters  remain  in  the  flask,  pour  the  entire 


LEAD.  151 

mixture  in  the  beaker  into  the  flask  and  then  back  into  the 
beaker  again  and  finish  the  titration  2  drops  at  a  time.  When 
the  final  yellow  tinge  is  obtained,  some  of  the  immediately 
preceding  tests  may  have  developed  a  tinge  also.  From  the 
reading  of  the  burette  deduct  the  volume  of  2  drops  for  each 
test  thus  showing  a  color.  Multiply  the  corrected  reading  by  the 
percentage  value  of  i  cc.  of  the  molybdate  solution  in  lead  to 
obtain  the  percentage  of  lead  in  the  ore. 

13.  Standard  Molybdate  Solution.  —  This  should  contain 
about  4.74  grams  of  ammonium  molybdate  per  liter,  in  order 
that  when  0.5  gram  of  ore  is  taken  for  assay  i  cc.  shall  equal 
about  i  per  cent,  of  lead. 

Standardize  as  follows:  Weigh  carefully  about  0.2  gram  of 
pure  lead  foil  and  dissolve  in  an  8-oz.  flask  by  warming  with  a 
mixture  of  2  cc.  of  strong  nitric  acid  and  4  cc.  of  water.  When 
dissolved,  boil  nearly  or  quite  to  dryness,  add  about  30  cc.  of 
water,  and  see  that  all  the  lead  nitrate  dissolves.  Now  add  5  cc. 
of  strong  sulphuric  acid,  boil  the  mixture  a  moment,  cool  to  room 
temperature,  and  allow  to  stand  and  settle  a  short  time.  Filter 
and  wash  with  dilute  (i :  10)  sulphuric  acid.  Proceed  with  the 
filtered  lead  sulphate  precisely  as  described  for  the  assay  of  an 
ore  (in  9  et  seq.),  except  that  the  purification  of  the  lead  sul- 
phide described  in  10  may  be  omitted.  I  formerly  dissolved 
the  lead  sulphate  directly  in  a  hot  solution  of  ammonium  chloride 
and  acetate  and  titrated  at  once.  It  was  observed,  however, 
that  the  large  amount  of  ammonium  salts  necessary  to  effect 
complete  solution  of  the  lead  sulphate  hindered  the  separation 
of  lead  as  molybdate  during  the  titration,  and  the  end-point  was 
not  as  sharp  as  that  obtained  by  the  method  described. 

Divide  the  weight  of  lead  taken  by  the  number  of  cubic  centi- 
meters of  molybdate  solution  used.  This  will  give  the  weight 
of  lead  corresponding  to  i  cc.  of  molybdate.  From  this  figure 


152  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

calculate  the  percentage  value  of  i  cc.  on  the  basis  of  0.5  gram 
of  ore  taken  for  assay,  i  cc.  of  the  molybdate  solution  should 
thus  equal  about  0.005  gram  of  lead,  or  about  i  per  cent. 

14.  Shorter  Method  for  Ores  containing  Little  or  No  Cal- 
cium. —  Alexander's  original  method  did  not  sufficiently  provide 
for  the  presence  of  calcium,  which  is  a  frequent  constituent  of 
lead  ores.     It  was  partially  to  avoid  this  source  of  error  that 
the  method  was  modified  as  above.     Calcium  forms  a  molybdate 
which  is  more  or  less  insoluble  under  the  conditions  of  the  titra- 
tion  and  tends  to  raise  the  results  in  a  rather  irregular  manner. 
When  it  is  known  to  be  absent,  or  present  only  in  small  amount 
(as  may  frequently  be  noted  from  the  appearance  of  the  lead 
sulphate  on  the  filter),  the  above  process  may  be  shortened  as 
follows : 

15.  Begin  as  usual  and  proceed  until  the  washed  lead  sul- 
phate precipitate  is  obtained  on  the  filter.     Place  the  precipitate 
and  filter  in  the  original  flask,  add  10  cc.  of  strong  hydrochloric 
acid  and  boil  until  the  filter  is  well  disintegrated,  then  add  15  cc. 
of  strong  hydrochloric  acid,  25^0:.  of  cold  water  and  25  cc.  of 
strong  ammonia  water.     Now  color  with  a  little  litmus  solution, 
make  slightly  alkaline  with  ammonia  if  not  already  so,  and  then 
make  distinctly  acid  with  strong  acetic  acid.     Heat  to  boiling 
and  see  that  the  lead  sulphate  is  entirely  dissolved,  then  dilute  to 
about  200  cc.  with  boiling- hot  water  and  titrate  as  previously 
described  (12). 

1 6.  Even  in  the  absence  of  calcium  this  method  is  liable  to  be 
unsatisfactory.     The   lead   sulphate   precipitate   will    frequently 
retain  iron  that  cannot  be  dissolved  or  washed  out,  but  which 
finally  goes  into  solution  with  the  lead  sulphate  and  gives  a 
color  with  tannic  acid  on  the  test-plate.     The  large  amount  of 
salts  present  also  obscures  the  end-point  and  hinders  the  precipi- 
tation of  the  lead  molybdate.     This  is  especially  noticeable  with 


LEAD.  153 

very  low  grade  ores.  Except,  therefore,  for  hasty  approximate 
results,  it  is  generally  best  to  use  the  somewhat  longer  method 
first  given. 

17.  Special    Treatment    for    Roasted    Products.  —  Roasted 
products  are  liable,  to  have  some  of  the  lead  in  the  form  of  a 
silicate    that   resists    the   ordinary   treatment    with   acids.     The 
following  method   of  procedure   has   been   found   successful   in 
such  cases: 

Treat  the  material  in  the  usual  way,  with  the  addition  of  about 
3  cc.  of  strong  hydrofluoric  acid.  Ordinarily,  this  is  all  that  is 
necessary.  If  there  is  much  carbonaceous  matter  the  mixture 
should  be  again  filtered  after  treatment  with  the  extraction  solu- 
tion. In  doubtful  cases,  reserve  this  filtrate,  hot,  instead  of 
proceeding  with  it,  until  the  insoluble  residue  on  the  filter  can  be 
further  treated  as  follows: 

Wash  the  filter  and  residue  well  with  hot  water  (to  remove 
sodium  acetate)  and  then  ignite  them  at  a  low  temperature  in  a 
platinum  dish.  The  amount  of  lead  present  is  usually  too  small  to 
occasion  any  danger  to  the  dish.  When  the  paper  is  burned  off, 
cool,  add  a  little  ammonium  nitrate  and  ignite  gently  once  more. 
When  cool,  add  about  3  cc.  of  hydrochloric  acid,  3  cc.  or  more 
of  pure  strong  hydrofluoric  acid,  and  a  few  drops  of  strong  sul- 
phuric acid.  Evaporate  cautiously  until  the  sulphuric  acid  is 
fuming  strongly,  then  cool,  dilute  with  a  little  water  and  heat 
to  boiling.  Keep  hot  until  any  anhydrous  ferric  sulphate  has 
entirely  dissolved,  then  cool  to  room  temperature  and  filter, 
washing  with  the  usual  dilute  sulphuric  acid.  Extract  the  lead 
sulphate  on  the  filter  with  hot  extraction  solution,  receiving  the 
filtrate  in  the  flask  containing  the  main  portion.  Finish  from  this 
point  in  the  regular  way,  according  to  the  method  employed. 

18.  Determination  of  Lead  in  the  Fire  Assay  Button.— Hammer 
or  roll  the  button  Out  thin  and  weigh  0.250  gram.     Dissolve  by 


154  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

warming  in  an  8-oz.  flask  with  a  little  i :  2  nitric  acid.  When 
dissolved,  boil  nearly  to  dryness,  add  about  30  cc.  of  water  and 
see  that  all  the  lead  nitrate  dissolves.  Some  lead  sulphate,  due 
to  sulphur  in  the  lead  button,  may  remain  insoluble.  Proceed 
from  this  point  as  described  in  7  or  13,  according  to  the  method 
adopted.  Calculate  the  percentage  of  lead  in  the  button  and 
correct  the  fire  assay  accordingly. 


CHAPTER  XVII. 

MAGNESIUM. 

i.  Method  for  Ores,  etc.— Treat  0.5  gram  of  the  ore  in  an 
8-oz.  flask  with  10  cc.  of  strong  hydrochloric  acid,  heating  gently, 
avoiding  boiling,  to  dissolve  oxides,  etc.  Then,  if  sulphides  are 
also  present,  add  5  cc.  of  strong  nitric  acid  and  continue  the 
gentle  heating  until  they  are  decomposed.  Now  boil  to  dryness 
to  expel  the  acids  (and  render  any  separated  silica  insoluble). 
Warm  the  residue  with  25  cc.  of  water  and  i  or  2  cc.  of  strong 
hydrochloric  acid,  to  effect  solution  of  the  salts,  then  transfer 
to  a  beaker,  dilute  to  about  150  -cc.  with  cold  water  and  pass  in 
hydrogen  sulphide  gas  to  remove  copper,  lead,  etc.  Filter, 
washing  with  dilute  hydrogen  sulphide  water,  and  receive  the 
filtrate  in  a  large  casserole  (5J-inch).  Boil  to  expd  the  hydro- 
gen sulphide  and  then  oxidize  the  iron  by  the  cautious  addition 
of  a  few  cubic  centimeters  of  strong  nitric  acid  to  the  boiling 
liquid.  Now  add  5  cc.  of  strong  hydrochloric  acid  (to  provide 
for  the  formation  of  sufficient  ammonium  chloride  to  prevent 
the  subsequent  precipitation  of  alkaline  earths  as  carbonates), 
then  15-20  cc.  of  strong  bromine  water  (to  remove  manganese), 
and  finally  make  alkaline  with  ammonia.  Boil  for  a  few 
moments,  allow  to  settle  somewhat,  and  then  filter,  washing  with 
hot  water.  Reserve  the  filtrate.  Continue  from  this  point  as 
described  for  calcium  in  x,  2  and  x,  3,  until  the  filtrate  from  the 

•55 


156  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

calcium  oxalate  is  obtained,  or  the  combined  filtrates,  if  two  pre- 
cipitations were  made.") 

2.  In    my   own    laboratory,    for    ordinary    technical    work, 
especially  when  the  amount  of  magnesium  is  supposed  to  be 
small,  this  filtrate  is  concentrated  considerably  by  boiling  in  a 
large  porcelain  casserole  and  the  magnesium  is   then   precipi- 
tated by  Handy 's  method    (10).     The   precipitated   magnesium 
ammonium  phosphate  is  then  ignited  and  weighed  as  Mg2P2O7, 
as  described  in  4. 

For  more  exact  results  proceed  as  follows: 

3.  Concentrate    the    filtrate    from    the   calcium   oxalate    to 
small  bulk  by  boiling  in  a  large  porcelain  casserole,  and  when 
salts  show  a  tendency  to  separate,  transfer  to  a  platinum  dish  or 
smaller  porcelain  casserole,  in  separate  small  portions  if  neces- 
sary,  and   evaporate   on   the   water-bath   to   complete   dryness. 
When  dry,  ignite  gently  to  expel  the  ammonium  salts.     Cool, 
dissolve  the  residue  in  a   very  little  dilute  hydrochloric  acid, 
make  very  faintly  alkaline  with  ammonia  and  filter  if  necessary. 
The  magnesium  is  now  precipitated  by  the  method  of  W.  Gibbs.*f 

4.  Heat    the    solution    to  boiling  and  add,  drop  by  drop,  a 
solution  of  sodium  ammonium  phosphate  (NaNH4HPO4.2H2O), 
1 60  grams  to  the  liter, J  until  no  further  precipitate  is  produced. 
Most  of  the  magnesium  is  at  once  precipitated  as  amorphous, 
dimagnesium  phosphate  (MgHPC^).     Allow  the  solution  to  cool, 
and  then,  stirring  constantly,  add  about  one- third  its  volume  of 
ammonia.     By  this  procedure  the  precipitate  is  changed  to  crys- 
talline magnesium  ammonium  phosphate  (MgNH4PO4)  and  the 
magnesium  remaining  in  solution  is  precipitated  in  the  same 

*  Am.  Jour.  Sci.,  (3)  5,  114. 

f  I  usually  prefer  to  precipitate  by  Handy's  method,   finally  weighing  the 
pyrophosphate,  however,   as  described  by  Gibbs. 

|  27  cc.  of  this  solution  will  precipitate  0.5  gram  of  magnesium. 


MAGNESIUM.  157 

form.  Let  the  cold  mixture  stand  2  or  3  hours  and  then  decant 
the  supernatant  solution  through  a  filter.  Wash  the  precipitate 
three  times  by  decantation  with  2j  per  cent,  ammonia  and  then 
transfer  to  the  filter  and  wash  thoroughly  with  2j  per  cent, 
ammonia.  Dry  the  filter  and  precipitate,  transfer  the  latter  as 
completely  as  possible  to  a  weighed  platinum  crucible,  burn  the 
filter-paper  in  a  platinum  spiral  and  add  the  ash  to  the  precipi- 
tate in  the  crucible.  Cover  the  crucible  and  heat  it,  gently  at 
first  to  expel  the  ammonia,  and  then  over  the  blast-lamp  until 
the  residue  is  pure  white.  Cool  in  desiccator  and  weigh  as 
Mg2P2O7.  This  weight,  multiplied  by  0.2188  will  give  that  of 
the  Mg,  or,  if  multiplied  by  0.3624,  that  of  the  MgO. 

5.  In    the   above  method  it  is  not  usually  considered  neces- 
sary to  remove,  as  sulphide,-  any  zinc  present,  inasmuch  as  the 
ignition  to  expel  ammonium  salts  will  tend  to  drive  off  the  zinc 
as  chloride.     Should  a  little  still  remain,  it  is  not  likely  to  precipi- 
tate as  phosphate  on  account  of  the  presence  of  the  ammonium 
and  ammonium  salts  added. 

6.  Note    on    the    Precipitation    of   Magnesium    Ammonium 
Phosphate.  —  If  the  precipitation  is  made  in  a  strongly  ammoni- 
acal  solution  instead  of  as  described,  some  tribasic  magnesium 
phosphate  (Mg3P2Os)  will  almost  invariably  form.     This  will  be 
unchanged  by  the  ignition  and  cause  low  results.     It  is,  therefore, 
necessary  to  add  the  excess  of  ammonia  later,  but  even  in  this 
case,  if  ammonium  salts  are  present,  the  precipitate  will  always 
contain    monomagnesium    ammonium    phosphate    (Mg(NH4)4 
(PO4)2),  which  requires  intense  heating  to  constant  weight  to  be 
certain  it  has  all  changed  to  Mg2P2Oj. 

7.  H.  Neubauer,*  whose  experiments  demonstrated  the  above 
facts,    proceeds    as    follows:     Slightly   acidify   the   filtrate   from 

*  Zeit.  f.  angew.  Chem.,  1896,  439.     Treadwell,  Quant.  Anal.,  Hall.,  zd  Ed., 
p.  65. 


158  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  calcium  oxalate  with  hydrochloric  acid  and  then  add  an  excess 
of  sodium  phosphate  solution  and  one-third  the  solution's  volume 
of  10  per  cent,  ammonia,  stirring  constantly.  Allow  to  stand  24 
hours  and  then  wash  by  decantation,  through  a  filter,  with  a 
little  2\  per  cent,  ammonia.  It  is  better  to  evaporate  the  filtrate 
from  the  calcium  oxalate  to  dryness  and  expel  the  ammonium 
salts  by  ignition,  as  previously  described  (3).  If  this  is  done, 
the  solution  may  be  filtered  after  only  4  hours'  standing  instead 
of  24.  Place  the  beaker  containing  most  of  the  precipitate  under 
the  funnel  and  pour  through  the  filter  a  little  dilute  hydrochloric 
acid,  washing  the  filter  with  hot  water.  Enough  acid  should  be 
used  to  effect  the  solution  of  the  precipitate  in  the  beaker.  Add 
now  some  ammonium  chloride,  a  few  drops  of  sodium  phosphate 
solution,  and  one-third  of  the  solution's  volume  of  10  per  cent, 
ammonia.  Allow  to  stand  4  hours.  Pour  the  solution  through 
a  filter,  wash  the  precipitate  three  times  by  decantation  with  2\ 
per  cent,  ammonia,  then  transfer  it  to  the  filter  and  wash  it 
thoroughly  with  the  dilute  ammonia.  Dry  and  ignite  the  pre- 
cipitate as  previously  described  (4). 

8.  Limestones,  Silicates,  etc. — In  material  of  these  classes 
the  members  of  the  hydrogen  sulphide  group  are  usually  absent, 
and,  accordingly,  no  steps  are  necessary  to  remove  them.  When 
the  substance  is  decomposable  by  acids  the  procedure  is,  with 
this  exception,  the  same  as  previously  described  for  ores  (i). 
The  treatment  of  silicates  is  begun  as  described  for  calcium  on 
similar  material  (x,  7),  but  inasmuch  as  the  magnesium  is  to  be 
determined  gravimetrically  it  is  necessary  to  evaporate  the  acid 
solution  to  dryness,  and  remove  the  silica  with  the  usual  precau- 
tions (xxiv,  n).  The  acid  solution,  free  from  silica,  is  then 
treated  as  described  for  ores,  usually  omitting  the  hydrogen 
sulphide  treatment. 


MAGNESIUM. 


'59 


9.  Handy's   Volumetric  Method.*  —  This  is  a  modification 
of  Stolba's  method  in  which  the  precipitated  magnesium  am- 
monium  phosphate   is   titrated   with   standard   sulphuric   acid, 
the  reaction  being 

MgNH4PO4  +  H2SO4  =  MgSO4  +  NH4H2PO4. 

A  measured  excess  of  sulphuric  acid  is  used  and  titrated  back 
with  standard  sodium  hydroxide.  The  results  obtained  are 
very  satisfactory. 

The  ore  or  other  material  is  treated  by  the  usual  methods 
and  the  nitrate  from  the  calcium  oxalate  precipitation  is  then 
treated  as  follows: 

10.  Add  ammonia  (sp.  gr.  0.90)  equivalent  to  i/io  of  the 
solution.     Cool  in  water  to  20°  to  25°  C.    Precipitate  by  adding 
slowly  with  constant  stirring  a  saturated  solution  of  sodium, 
ammonium  phosphate,  using  i  cc.  for  each  o.oi  gram  magnesium 
oxide.     Stir  vigorously  for  5  minutes  or  shake  in  a  flask  for  an 
equal  length  of  time.     In  the  former  case  let  the  solution  stand 
until  the  clarification  of  the  upper  liquid  shows  that  the  reaction 
is  complete.     In  the  case  of  flask  precipitations,  if  over  0.002 
gram  of  magnesium  oxide  is  present  the  solution  may  be  filtered 
in  15  minutes.     Suction  may  be  used  if  desired,  but  if  many 
solutions  are  to  be  filtered  at  once  little  is  gained  by  its  use. 
Use  10  per  cent,  ammonia  wash  (i  part  ammonia  (sp.  gr.  0.90) 
to  9  of  water).     Deliver  it  preferably  from  an  aspirator  bottle 
placed  about  4  feet  above  the  bench.     Wash  by  decantation  as 
far  as  possible.     Finally,  wash  the  precipitate  which  has  gone 
on  the  filter  back  into  the  beaker,  stir  it  up  with  the  ammonia 
wash  and  bring  it  again  completely  on  the  filter-paper.     Wash 
once  more,  leaving  the  upper  edge  of  the  filter  clear  of  precipitate 
so  that  it  can  be  handled.     Avoid  assembling  all  of  the  precipitate 

*  James  Otis  Handy,  Jour.  Am.  Chem.  Soc.,  XXII,  p.  31. 


160  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

in  the  apex,  but  leave  it  fairly  evenly  distributed  over  the  lower 
two-thirds  of  the  paper.  Allow  the  precipitates  to  drain  and 
then  transfer  each  in  turn  to  a  dry  5-inch  filter-paper,  allowing 
them  to  remain  there  open  and  face  upward  until  the  bulk  of 
the  moisture  has  been  absorbed.  After  about  3  minutes  trans- 
fer them  to  fresh  dry  niters,  and  in  the  case  of  heavy  precipitates 
to  a  third  set  a  few  minutes  later.  Then  place  the  filters  on  a 
shelf  to  dry  at  the  temperature  of  the  room,  or  place  filter-papers 
and  backing  on  the  grating  of  an  air-oven  having  a  temperature 
of  50°  to  60°  C.  After  15  or  20  minutes  in  the  oven,  or  45  min- 
utes in  the  air,  watch  for  the  time  when  the  filters  have  dried 
inward  half  an  inch  from  the  margin.  This  appearance  has 
been  found  to  indicate  that  the  evaporation  has  gone  far  enough 
to  insure  the  expulsion  of  the  free  ammonia.  Now  place  the  pre- 
cipitates and  filters  in  small  dry  beakers  and  treat  each  with  a 
measured  excess  of  decinormal  sulphuric  acid,  stirring  until  the 
papers  are  disintegrated  and  the  precipitates  dissolved.  Then 
add  2  drops  of  a  o.i  per  cent,  alcoholic  solution  of  methyl  orange. 
If  this  gives  a  clear  decided  pink,  enough  acid  has  been  added. 
If  it  is  only  faintly  pink,  the  excess  of  acid  is  slight  and  some 
minute  particles  may  have  escaped  solution.  In  such  cases  add 
5  cc.  more  decinormal  sulphuric  acid  and  stir  well.  Finally, 
dilute  to  about  100  cc.  and  titrate  back  with  decinormal  sodium 
hydroxide  solution  to  the  appearance  of  a  clear  yellow  color,  free 
from  all  suggestion  of  pink. 

i  cc.  N/io  H2SC>4  =0.002  gram  MgO. 

If  the  nitrations  have  taken  place  during  the  latter  part  of  the 
day,  the  filters  may  be  removed  from  the  funnels  and  allowed 
to  stand  overnight,  after  which  they  are  titrated  as  described. 

ii.    Notes    on   the   above  Method  (Handy). — If  the  drying 
of  the  precipitate  proceeds  too  far,  solution  in  decinormal  sul- 


MAGNESIUM.  161 

phuric  acid  is  slow.  If,  however,  the  drying  is  stopped  at  the 
point  described,  there  is  enough  moisture  left  so  that,  on  stirring, 
the  precipitate  blends  quickly  with  the  acid  and  soon  dissolves. 
The  tendency  of  magnesium  to  precipitate  with  iron  and 
aluminum  and  with  calcium  oxalate  must  be  met  by  re-solution 
in  hydrochloric  acid  and  reprecipitation.  When  the  amount  of 
calcium  is  considerable  it  is  best  to  burn  off  the  first  oxalate 
precipitate  before  dissolving  in  hydrochloric  acid.  By  this 
means  the  oxalate  is  decomposed  and  the  addition  of  ammonia 
alone  does  not  cause  its  sudden  reprecipitation.  Even  in  the 
second  precipitation,  if  the  boiling  is  allowed  to  proceed  longer 
than  is  necessary  to  make  the  finely  crystalline  calcium  oxalate 
settle  well,  some  magnesium  oxalate  is  sure  to  precipitate,  betray- 
ing its  presence  by  its  coarser  texture.  The  solution  for  mag- 
nesium precipitation  usually  does  and  always  should  contain  in 
the  form  of  ammonium  chloride  the  equivalent  of  5  cc.  of  con 
centrated  hydrochloric  acid  per  100  cc. 


CHAPTER  XVIII. 
MANGANESE. 

1.  THE    following  methods  for  the  determination  of  man- 
ganese are  applicable  to  most  ores,  the  first  one  being  ordinarily 
employed  in  my  own  laboratory.     In  unusual  cases,  where  the 
material  fails  to  be  sufficiently  decomposed  by  simple  acid  treat- 
ment, the  mode  of  attack  calls  for  the  exercise  of  the  operator's 
judgment.     It  is  usual  in  such  cases  to  employ  one  of  the  methods 
described  under  IRON    (xv,    17,  18,  et  seq.),  and  eventually  to 
bring  the  solution  of  the  substance  into  a  proper  condition  for 
continuing  by  the  regular  method. 

2.  Usual    Method    for    Ores,    etc. — Treat  0.5   gram  of  the 
substance  in  an  8-oz.  flask  with  whatever  acids  are  necessary 
to  decompose  it.     For  an  oxidized  ore,  about  10  cc.  of  strong 
hydrochloric  acid  are  usually  sufficient.     With  mixed  ores  it  is 
best,  in  most  cases,  to  start  with  hydrochloric  acid,  to  dissolve 
the  oxides,  and  then  add  5-10  cc.  of  strong  nitric  acid  to  decom- 
pose the  sulphides.     With  pure,  or  nearly  pure,  sulphides,  begin 
at  once  with  10  cc.  of  nitric  acid. 

3.  Heat  very  gently  at   first  until  the  decomposition  is  com- 
plete.    Finally  add  about   5  cc.   of  strong  sulphuric   acid  and 
heat  strongly,  best  over  a  free  flame,  until  only  a  very  little 
sulphuric  acid  remains.     Cool  and  add  about  100  cc.  of  water. 

Boil  the  mixture  a  moment  and  allow  to  stand,  hot,  with  occa- 

162 


MANGANESE.  163 

sional  shaking,  until  anhydrous  ferric  sulphate,  etc.,  has  dis- 
solved. Now  add  an  excess  of  zinc  oxide  in  thick  emulsion.* 
Avoid  a  large  excess,  but  add  sufficient  to  precipitate  all  the  iron, 
so  that  on  standing  a  moment  the  mixture  begins  to  settle  clear 
and  some  zinc  oxide  can  be  seen  in  the  bottom  of  the  flask,  f 
The  mixture  should  be  agitated  to  facilitate  the  precipitation, 
and  it  is  best  to  boil  it.  Filter,  wash  thoroughly  with  hot  water 
and  receive  the  nitrate  in  a  5oo-cc.  beaker. 

4.  Instead   of   precipitating   and   filtering  as  above,  the  fol- 
lowing procedure  is  usually  much  quicker  and  quite  accurate 
enough   for   technical   purposes:    Transfer   the    solution    of   the 
sulphates  to  a  2oo-cc.  measuring-flask,  using  hot  water.     Now 
add  the  zinc  oxide  as  described  and  then  cool  the  mixture  to 
room  temperature  under  the  tap.     Make  up  to  the  mark  with 
cold  water,  mix  thoroughly  and  then  filter  off  100  cc.  through  a 
dry  filter  into  a   loo-cc.  measuring-flask.      Or,  allow  to  settle 
sufficiently  and  remove   100  cc.  with  a  pipette.    Transfer  the 
100  cc.  to  a  5OO-CC.  beaker. 

5.  To  the  solution  in  the  large  beaker  add  3-4  grams  of  sodium 
acetate  and  about  25  cc.  of  saturated  bromine  water.     Boil  the 
mixture  several  minutes,  adding  more  bromine  water  if  there  does 
not  appear  to  be  an  excess.     Allow  the  precipitate  to  settle  some- 
what and  then  filter  and  wash  thoroughly  with  hot  water.     The 
filtrate  should  be  clear  and  may  be  tested  further,  if  desired,  by 
adding  more  bromine  water  and  boiling.     A  clear  yellowish  filtrate 

*  For  ordinary  use  I  simply  mix  the  usual  C.  P.  zinc  oxide  with  water.  A 
better  and  purer  mixture  is  made  as  follows:  Precipitate  a  solution  of  pure  zinc 
sulphate  with  a  solution  of  potassium  hydroxide  in  insufficient  amount  to  cause 
the  solution  to  become  alkaline.  Wash  the  residue  several  times  with  hot  water 
and  then  transfer  it  to  a  tightly  stoppered  bottle  with  enough  water  to  hold  it  in 
suspension. 

f  If  lead  is  present  a  little  will  remain  in  solution  and  be  counted  as  manganese. 
It  may  be  removed  by  adding  2  or  3  cc.  of  strong  solution  of  potassium  dichromate 
at  this  stage. 


1 64  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

usually  indicates  that  the  manganese  has  been  all  precipitated, 
the  yellow  color  showing  an  excess  of  bromine. 

6.  Place  the  washed  precipitate,  together  with  the  filter,  back 
in  the  beaker  and  run  in  from  a  burette  what  is  judged  to  be 
an  excess  of  the  standard  oxalic  acid  solution  described  below 
(9).  On  the  basis  of  0.5  gram  of  ore  taken  for  assay,  each  cubic 
centimeter  of  this  solution  is  equivalent  to  about  i  per  cent,  of 
manganese.  Now  add  about  50  cc.  of  dilute  (1:9)  sulphuric  acid 
and  heat  the  mixture  nearly  to  boiling  with  gentle  agitation. 
Avoid  shredding  the  filter.  If  the  precipitate  fails  to  dissolve 
completely,  add  more  of  the  oxalic  acid  solution  but  avoid  a 
large  and  unnecessary  excess.  When  the  precipitate  has  entirely 
dissolved,  dilute  the  solution  to  150-200  cc.  with  hot  water  and 
titrate  to  a  faint  permanent  pink  tinge  with  a  standard  solution 
of  potassium  permanganate  (8).  The  excess  of  oxalic  acid  not 
consumed  by  the  MnC>2  is  thus  found.  Subtracting  this  from 
the  total  amount  of  oxalic  acid  used,  the  remainder  is  the  amount 
used  in  reducing  the  MnO2  to  MnO.  Multiply  this  figure  by 
the  value  of  i  cc.  in  manganese  to  obtain  the  amount  of  man- 
ganese in  the  ore. 

Example. — Took  0.5  gram  of  ore  and  did  not  divide  the 
solution. 

i  cc.  of  the  permanganate  solution  =  0.5611  cc.  of  the  oxalic  acid  sol. 

i  cc.  of  the  oxalic  acid  solution  =  0.00502  gram  of  manganese,  or, 
1.04  percent,  when  0.5  gram  of  ore  is  taken. 

Permanganate  used  in  titrating  excess  of  oxalic  acid,  5.65  cc., 
equivalent  to  3.17  cc.  of  oxalic  acid  solution. 

Total  number  of  cc.  of  oxalic  acid  solution  used..  25.40 
Less  excess 3.17 


Consumed  by  the  MnC>2 22.23 


MANGANESE..  165 

22.23  multiplied  by  1.04  gives  23.12,  the  percentage  of  manganese 
in  the  ore.  If  the  solution  had  been  divided,  the  figure  thus 
obtained  would  have  to  be  multiplied  by  2. 

7.  The  reactions  that  take  place  may  be  expressed  as  fol- 
lows: 

Between  the  MnO2  and  the  oxalic  acid: 


Thus  126.048  parts,  by  weight,  of  oxalic  acid  in  the  standard 
solution  correspond  to  55  parts  of  manganese,  i  per  cent,  of 
manganese,  on  the  basis  of  0.5  gram  of  ore  taken  for  assay,  is 
0.005  gram,  and  the  amount  of  oxalic  acid  corresponding  to  this 
is  0.011458  gram.  This,  then,  is  the  amount  to  be  contained 
in  i  cc.,  or,  11.458  grams  per  liter,  in  order  that  i  cc.  =  i  per  cent. 
Mn. 

Between  the  oxalic  acid  and  permanganate: 


=  K2SO4  +  2MnSO4  +  ioCO2  +  ioH2O. 

The  standard  solutions  required  are  prepared  as  follows: 
8.  Standard  Potassium  Permanganate.  —  This  may  be  approxi- 
mately one-  tenth  normal,  or  about  3.16  grams  per  liter.  The 
solution  used  for  iron  is  ordinarily  employed.  The  iron  value 
multiplied  by  1.128  will  give  the  oxalic  acid  value.  This  value 
may  also  be  determined  by  standardizing  against  oxalic  acid  or 
an  oxalate  directly.  While  the  usual  C.  P.  oxalic  acid  is  not 
absolutely  pure,  it  will  generally  suffice  for  technical  work. 
Weigh  carefully  about  0.2  gram  of  the  clean  crystals  and  dis- 
solve in  a  6-oz.  flask  in  a  mixture  of  about  5  cc.  of  strong  sul- 
phuric acid  and  100  cc.  of  water.  Heat  to  6o°-7o°  C.  and 
titrate  with  the  permanganate  solution  to  a  permanent  faint 
pink  tinge.  From  the  number  of  cubic  centimeters  used  cal- 
culate the  value  of  i  cc.  in  oxalic  acid. 


i66  TECHNICAL  METHODS    OF  ORE   ANALYSIS. 

Example. — Took  0.2195  gram  of  oxalic  acid.  Used  34.000. 
of  permanganate.  Then  0.2195-^-34.0  =  0.006455,  the  value  in 
grams  of  oxalic  acid  of  i  cc.  of  the  permanganate  solution,  i  cc. 
of  an  exactly  decinormal  permanganate  solution  would  equal 
0.0063024  gram  of  oxalic  acid. 

9.  Standard  Oxalic  Acid  Solution. — This,  as  explained  above 
(7),  should  contain  about  11.46  grams  of  C2O4H2.2H2O  per 
liter,  in  order  that  i  cc.  may  equal  about  i  per  cent,  of  man- 
ganese when  0.5  gram  of  ore  is  taken  for  assay.  Standardize  as 
follows:  Place  in  an  8-oz.  flask  about  5  cc.  of  strong  sulphuric 
acid  and  dilute  with  100  cc.  of  water.  From  a  burette  run  in 
about  25  cc.  of  the  oxalic  acid  solution.  Heat  the  mixture  to 
about  70°  C.  and  titrate  with  the  standard  permanganate  to  a 
permanent  faint  pink  tinge.  From  the  number  of  cubic  centi- 
meters of  permanganate  used,  and  the  known  value  of  each  cubic 
centimeter  in  oxalic  acid,  calculate  the  true  strength  of  the  oxalic 
acid  solution  and  the  consequent  value  of  i  cc.  in  manganese. 

Example. — Ran  in  21.70  cc.  of  oxalic  acid  solution.  Used 
40  cc.  of  permanganate.  If  the  value  of  i  cc.  of  permanganate 
is  0.006455  gram  of  C2O4H2.2H2O,  then  the  40  cc.  used  are 
equal  to  0.2582  gram.  As  this  is  the  amount  of  oxalic  acid 
contained  in  21.70  cc.,  each  cubic  centimeter  contains  0.0119 
gram.  In  the  reaction  between  manganese  dioxide  and  oxalic 
acid  previously  given  (7),  it  is  shown  that  126.048  parts  by  weight 
of  oxalic  acid  are  equal  to  55  parts  of  manganese.  Consequently, 
to  find  the  manganese  value  of  the  present  oxalic  acid,  we  have 
the  proportion 

126.048 : 55  =0.01 19  :x 

#  =  0.0052 

(Oxalic  acid  X 0.4364  =  Mn). 

i  cc.  of  the  oxalic  acid  solution  therefore  equals  0.0052  gram 
of  Mn,  or,  1.04  per  cent,  on  the  basis  of  0.5  gram  of  ore. 


MANGANESE.  167 

10.  In  determining  the  manganese  value  of  the  oxalic  acid 
solution,  the  value  of  i  cc.  of  the  permanganate  solution  in  cubic 
centimeters  of  standard  oxalic  acid  solution  should  also  be  noted. 
Thus,  in  the  last  example,  40  cc.  of  \  ermanganate  solution  were 
equal  to  21.70  cc.  of  oxalic  acid  solution,  therefore,  i  cc.  of  per- 
manganate solution  is  equal  to  0.5425  cc.  of  oxalic  acid  solution. 
This  value  should  be  marked  on  the  permanganate  bottle.     The 
oxalic    acid   solution   very   slowly  decomposes  on  keeping  and 
requires  to    be   restandardized   occasionally.      The  addition  of 
50  cc.  of   sulphuric  acid  per  liter   greatly  improves  its  keeping 
qualities. 

11.  Volhard's   Method. — This  is  the  method  most  generally 
used  in  western  laboratories.     Treat  i  gram  of  the  ore  in  an  8-oz. 
flask  with  whatever  acids  are  necessary  to  decompose  it,  beginning 
with  10  cc.  of  strong  hydrochloric  acid,  and  heating  very  gently,  if 
oxides  are  present,  and  afterwards  adding  nitric  acid,  if  necessary, 
to  decompose  sulphides  and  peroxidize  iron.     When  the  decom, 
position  is  complete   add  about  7  cc.  of  strong  sulphuric  acid 
and  heat  over  a  free  flame  until  fumes  of  sulphuric  anhydride  are 
evolved  copiously.     Cool,  add  25  cc.  of  water,  boil  a  short  time, 
and  allow  to  stand,  hot,  with  frequent  shaking,  until  any  anhydrous 
ferric  sulphate  has  all  dissolved.     Transfer  the  mixture  to  a  500-0:. 
graduated  flask  and  add  an  emulsion  of  zinc  oxide*  in  slight 
excess  to  precipitate   the   iron.     Agitate   the   flask  to   facilitate 
the  precipitation  and  see  that  a  slight  excess  of  zinc  oxide  remains 
when  the  reaction  is  complete.     Now  dilute  the  contents  of  the 
flask  up  to  the  mark  with  cold  water,  mix  thoroughly  and  allow 
to  stand  a  short  time  and  partially  settle.     By  means  of  a  grad- 
uated  pipette   draw  off  100  cc.  of  the  clear  supernatant  liquid 

transfer  it  to  an  8-oz.  flask.     While  the  precipitate  in  the 

*  See  foot-note  to  3. 


1  68  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

500-cc.  flask  may  appear  large,  it  actually  occupies  but  a  very 
small  space,  and  any  error  caused  by  it  may  consequently  be 
neglected.  Likewise  the  error  in  measurement  due  to  change 
of  temperature  during  the  manipulation  is  insignificant.  Heat 
the  solution  in  the  small  flask  to  boiling,  add  two  or  three  drops 
of  nitric  acid  (which  causes  the  subsequent  precipitate  to  settle 
more  quickly)  and  titrate  with  a  standard  solution  of  potassium 
permanganate.  The  permanganate  causes  a  precipitate  which 
obscures  the  liquid,  and  it  is  therefore  necessary  to  titrate  cau- 
tiously and  agitate  the  flask  after  each  addition,  and  then  allow 
the  precipitate  to  settle  sufficiently  to  observe  whether  or  not  the 
solution  is  colored  pink.  A  little  experience  will  enable  one  to 
judge  by  the  volume  of  the  precipitate  formed,  about  how  rapidly 
to  run  in  the  permanganate.  The  final  pink  tinge,  indicating 
the  end  of  the  reaction,  is  best  observed  by  holding  the  flask 
against  a  white  background  and  observing  the  upper  edges  of  the 
liquid.  When  this  point  is  attained,  bring  the  contents  of  the 
flask  nearly  to  a  boil  once  more  and  again  observe  if  the  pink 
tint  still  persists,  adding  more  permanganate  if  necessary.  In 
making  this  end-test  avoid  actually  boiling  the  liquid,  as  a  con- 
tinual destruction  of  the  color  may  sometimes  thus  be  effected 
and  the  true  end-point  considerably  passed.  When  the  color 
thus  remains  permanent  the  operation  is  ended.  Observe  the 
number  of  cubic  centimeters  of  permanganate  solution  used  and 
calculate  the  result. 

12.  The  precipitate  formed  is  not  manganese  dioxide,  although 
the  calculation  can  be  correctly  made  as  though  the  following 
reaction  took  place: 


3MnSO4  +  2KMnO4  +  2H2O  =  sMnO2  +  K2SO  +  2H2SO4. 
In  the  presence  of  metallic  salts,  such  as  those  of  calcium  or 


MANGANESE.  169 

zinc,  manganites  of  varying  composition  are  formed,  e.g., 


=  4KHSO4  +  7H2SO  +  5ZnH2.2MnO3. 

The  precipitated  manganese  is,  however,  always  in  the 
tetravalent  form,  and,  therefore,  the  ratio  of  the  first  reaction 
between  the  manganese  and  the  permanganate  is  not  changed. 

13.  It  is  customary  to  use  the  same  permanganate  solution 
for  both  iron  and  manganese.     Having  determined  the  factor 
for  iron   (xv,  12),  this  may  be  multiplied  by  0.2952  to  obtain  the 
factor  for  manganese.     It  will  be  observed  in  the  first  equation 
above  that  2KMnO4  are  required  for  3Mn,  and  in  the  reaction 
for  iron  in  xv,  2,  that  2KMnO4  are  required  for  loFe.     There- 
fore 559  parts  of  iron  are  equivalent  to  165  parts  of  manganese, 
or,  i  part  of  iron  to  0.2952  part  of  manganese. 

14.  The  Bismuthate  Method  for  the  Determination  of  Man- 
ganese.* —  This  method  is  based  on  the  fact  that  a  manganous 
salt  in  the  presence  of  an  excess  of  nitric  acid  is  oxidized  to 
permanganic  acid  by  bismuth  tetroxide.     The  permanganic  acid 
formed  is  very  stable  in  nitric  acid  of  1.135  SP-  &1"-  when  the 
solution  is  cold,  but  in  hot  solutions  the  excess  of  the  bismuth 
tetroxide  is  rapidly  decomposed  and  then  the  nitric  acid  reacts 
with  the  permanganic  acid,  and  as  soon  as  a  small  amount  of 
manganous  salt  is  formed  the  remainder  of  the  permanganic  acid 
is    decomposed,    manganous    nitrate    dissolves    and    manganese 
dioxide  precipitates. 

In  the  cold,  however,  the  excess  of  the  bismuth  salt  may  be 
filtered  off  and  to  the  clear  filtrate  an  excess  of  ferrous  sulphate 

*  Andrew  A.  Blair,  Jour.  Am.  Chem.  Soc.,  XXVI,  793.  Method  originally 
proposed  by  Schneider  and  modified  first  by  Reddrop  and  Ramage  and  then  by 
Brearley  and  Ibbotson. 


170  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

added  and  the  amount  necessary  to  deoxidize  the  permanganic 
acid  determined  by  titrating  with  permanganate.  The  end 
reactions  are  very  sharp  and  the  method  is  extremely  accurate, 
but  the  presence  of  even  a  trace  of  hydrochloric  acid  utterly 
vitiates  the  results.  As  pointed  out  by  Reddrop  and  Ramage, 
bismuth  tetroxide,  which  was  used  by  Schneider,  is  difficult  to 
obtain  free  from  chlorides  and  they  recommended  sodium 
bismuthate,  which  they  prepare  as  follows:  Heat  20  parts  of 
caustic  soda  nearly  to  redness  in  an  iron  or  nickel  crucible  and 
add,  in  small  quantities  at  a  time,  10  parts  of  basic  bismuth 
nitrate,  previously  dried  in  a  water-oven.  Then  :add  2  parts  of 
sodium  peroxide  and  pour  the  brownish  yellow  fused  mass  on 
an  iron  plate  to  cool;  when  cold,  break  it  up  in  a  mortar,  extract 
with  water  and  collect  on  an  asbestos  filter.  The  residue,  after 
being  washed  four  or  five  times  by  decantation,  is  dried  in  the 
water-oven,  then  broken  up  and  passed  through  a  fine  sieve. 
(The  Baker  &  Adamson  Chemical  Co.  have  prepared  sodium 
bismuthate  in  this  manner  which  is  perfectly  free  from  man- 
ganese chlorides  and  has  proved  entirely  satisfactory.) 

The  Method. 

Steels.  —  Dissolve  i  gram  of  drillings  in  50  cc.  of  nitric  acid 
(sp.  gr.  1.135)  in  an  Erlenmeyer  flask  of  200  cc.  capacity.  Cool 
and  add  about  0.5  gram  of  bismuthate.  The  bismuthate  may 
be  measured  in  a  small  spoon,  and  experience  will  soon  enable 
the  operator  to  judge  of  the  amount  with  sufficient  accuracy. 
Heat  for  a  few  minutes,  or  until  the  pink  color  has  disappeared, 
with  or  without  the  precipitation  of  manganese  dioxide.  Add 
sulphurous  acid,  solution  of  ferrous  sulphate  or  sodium  thio- 
sulphate  in  sufficient  amount  to  clear  the  solution  and  heat  until 
all  nitrous  oxide  has  been  driven  off.  Cool  to  about  15°  C., 
add  an  excess  of  bismuthate  and  agitate  for  a  few  minutes. 


MANGANESE. 


171 


Add  50  cc.  of  water  containing  30  cc.  of  nitric  acid  to  the  liter 
and  filter  through  an  asbestos  felt  on  a  platinum  cone  into  a  300- 
cc.  Erlenmeyer  flask  and  wash  with  50  to  100  cc.  of  the  same 
acid.  The  arrangement  shown  in  Fig.  17  has  proved  very  satis- 
factory. Run  into  the  flask  from  the  pipette,  shown  in  Fig.  18, 


FIG.  17. 


FIG.  18. 


a  measured  volume  of  ferrous  sulphate  solution  and  titrate  to 
a  faint  pink  color  with  permanganate.  The  number  of  cubic 
centimeters  of  the  permanganate  solution  obtained,  subtracted 
from  the  number  corresponding  to  the  volume  of  ferrous 
sulphate  solution  used,  will  give  the  volume  of  permanganate 
equivalent  to  the  manganese  in  the  sample,  which,  multiplied  by 
the  value  of  the  permanganate  in  manganese,  gives  the  amount 
of  manganese  in  the  steel. 


172  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

Pig  Iron.  —  Dissolve  i  gram  in  25  cc.  of  nitric  acid  (sp.  gr. 
1.135)  m  a  small  beaker  and  as  soon  as  the  action  has  ceased, 
filter  on  a  7  cm.  filter  into  a  200  cc.  Erlenmeyer  flask,  wash  with 
30  cc.  of  the  same  acid  and  proceed  as  in  the  case  of  steels. 

In  the  analysis  of  white  irons  it  may  be  necessary  to  treat  the 
solution  several  times  with  bismuthate  to  destroy  the  combined 
carbon.  The  solution,  when  cold,  should  be  nearly  colorless;  if 
not,  another  treatment  with  bismuthate  is  necessary. 

Iron  Ores  Containing  Less  than  2  Per  Cent,  of  Manganese.  — 
Treat  i  gram  in  a  platinum  dish  or  crucible  with  4  cc.  of  strong 
sulphuric  acid,  10  cc.  of  water  and  10  to  20  cc.  of  hydrofluoric 
acid.  Evaporate  until  the  sulphuric  acid  fumes  freely.  Cool 
and  dissolve  in  25  cc.  of  1.35  nitric  acid.  If  no  appreciable 
residue  remains,  transfer  to  a  200  cc.  Erlenmeyer  flask,  using  25 
cc.  of  1.135  nitric  acid  to  rinse  the  dish  or  crucible  and  proceed 
as  usual.  If  there  is  an  appreciable  residue,  filter  on  a  small 
filter  into  a  beaker,  wash  with  water,  burn  the  filter  and  residue 
in  a  crucible  and  fuse  with  a  small  amount  of  potassium  acid 
sulphate.  Dissolve  in  water  with  the  addition  of  a  little  nitric 
acid,  add  to  the  main  filtrate,  evaporate  nearly  to  dryness,  take 
up  in  1.135  nitric  acid  and  transfer  to  the  flask  as  before. 

Manganese  Ores  and  Iron  Ores  High  in  Manganese.  —  Treat 
i  gram  as  in  the  case  of  iron  ores,  using  a  little  sulphurous  acid 
if  necessary.  Transfer  the  solution  to  a  500  cc.  flask,  dilute  to 
the  mark,  mix  thoroughly  and  measure  into  a  flask  from  a  care- 
fully calibrated  pipette  such  a  volume  of  the  solution  as  will  give 
from  i  to  2  per  cent,  of  manganese  and  enough  strong  nitric 
acid  (sp.  gr.  1.4)  to  yield  a  mixture  of  1.135  acid  in  a  volume 
of  50  to  60  cc.  For  example,  in  a  50  per  cent,  ore  use  10  cc.  of 
the  solution  and  add  30  cc.  of  water  and  10  cc.  nitric  acid 
(sp.  gr.  1.4).  In  this  case  the  manganese  must  be  calculated  on 
sV  of  a  gram  or  20  mg.  of  ore.  When  working  on  such  amounts 


MANGANESE.  173 

it  is  always  desirable  to  make  duplicate  analyses  and  take  the 
mean,  as  a  difference  of  o.  i  cc.  makes  a  large  error  in  the  result. 
When  the  ore  contains  a  much  smaller  amount  of  manganese, 
say  5  to  10  per  cent., f  it  is  better  to  make  up  the  solution  to  say 
100  cc.  instead  of  500. 

Ferro -manganese.  —  Treat  I  gram  exactly  like  steel.  Dilute 
to  500  or  1000  cc.  and  proceed  as  in  manganese  ores. 

Ferro-silicon.  —  Treat  i  gram  with  sulphuric  and  hydrofluoric 
acids  and  proceed  as  with  iron  ores. 

Special  Steels.  —  Steels  containing  chromium  offer  no  special 
difficulties  except  that  it  must  be  noted  that  while  in  hot  solu- 
tions the  chromium  is  oxidized  to  chromic  acid,  which  is  reduced 
by  the  addition  of  sulphurous  acid,  the  oxidation  proceeds  so 
slowly  in  cold  solutions  that  if  there  is  no  delay  in  the  nitration 
and  titration  the  results  are  not  affected.  Steels  containing 
tungsten  are  sometimes  troublesome  on  account  of  the  necessity 
for  getting  rid  of  the  tungstic  acid.  Those  that  decompose 
readily  in  nitric  acid  may  be  filtered  and  the  filtrate  treated  like 
pig  iron,  but  when  it  is  necessary  to  use  hydrochloric  acid  it  is 
best  to  treat  with  aqua  regia,  evaporate  to  dryness,  redissolve  in 
hydrochloric  acid,  add  a  few  drops  of  nitric  acid,  dilute,  boil,  and 
filter.  Get  rid  of  every  trace  of  hydrochloric  acid  by  repeated 
evaporations  with  nitric  acid  and  proceed  as  with  an  ordinary 
steel. 

Reagents. 

Nitric  Acid  (sp.  gr.  1.135).  —  A  mixture  of  3  parts  of  water 
and  i  part  strong  nitric  acid  answers  perfectly  for  this  purpose. 

•Nitric  Acid  (3  per  cent.).  —  Thirty  cc.  of  strong  nitric  acid  to 
the  liter. 

Permanganate  Solution  and  Ferrous  Sulphate  Solution. — One 
gram  of  potassium   permangate  to  the  liter   gives   a  solution  of 


174  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

convenient  strength,  and  12.4  grams  of  ferrous  ammonium  sul- 
phate and  50  cc.  of  strong  sulphuric  acid,*  made  up  to  i  liter, 
gives  a  solution  which  is  almost  exactly  equal  to  the  perman- 
ganate solution.  As  the  strength  of  the  ferrous  sulphate  solution 
changes  quite  rapidly,  while  the  permanganate  remains  unaltered 
for  months,  it  is  unnecessary  and  troublesome  to  attempt  to  keep 
them  of  the  same  strength.  By  using  a  constant  volume  of  the 
ferrous  sulphate  solution  and  testing  it  against  the  permanganate 
solution  every  day,  the  calculation  of  the  results  is  very  simple. 
It  is  necessary  that  the  conditions  should  be  the  same  in  getting 
the  strength  of  the  ferrous  sulphate  solution  as  in  titrating  a  solu- 
tion for  manganese,  and  after  many  experiments  the  following 
method  of  procedure  was  adopted:  Measure  into  a  200  cc.  flask 
50  cc.  of  nitric  acid  (sp.  gr.  1.135),  co°l  and  add  a  very  small 
amount  of  bismuthate,  dilute  with  50  cc.  of  3  per  cent,  nitric  acid, 
filter  into  a  300  cc.  flask  and  wash  with  50  cc.  of  3  per  cent,  nitric 
acid.  If  the  felt  is  well  coated  with  bismuthate  it  is  unnecessary 
to  add  any  to  the  nitric  acid  in  the  flask,  as  nitration  through  the 
mass  of  bismuthate  on  the  felt  will  answer  the  purpose.  Run  in 
from  the  pipette  (Fig.  18)  25  cc.  of  ferrous  sulphate  solution  and 
titrate  with  the  permanganate  to  a  faint  pink.  This  gives  the 
value  in  permanganate  of  the  ferrous  sulphate  solution.  With 
this  method  of  procedure  the  discrepancies  that  had  occurred 
entirely  disappeared,  and  it  is  possible  to  make  any  number  of 
determinations  with  a  variation  of  less  than  o.i  cc. 

The  permanganate  solution  may  be  standardized  in  three 
ways : 

First,  by  getting  its  value  in  iron  in  the  usual  way  and  calcu- 
lating its  value  in  manganese.  The  proportion  is  279.5  :  55>  or 
as  i:  0.1968. 

*  Dr.  C.  B.  Dudley  proposes  to  use  25  cc.  of  sulphuric  and  25  cc.  of  strong 
phosphoric  acid  as  tending  to  give  a  more  nearly  colorless  solution. 


MANGANESE.  !75 

Second,  by  titrating  a  steel  with  a  known  amount  of  manganese 
and  getting  the  value  of  the  solution  by  dividing  the  percentage 
of  manganese  by  the  number  of  cubic  centimeters  of  the  per- 
manganate used. 

Third,  by  making  a  solution  of  pure  manganese  sulphate  and 
determining  the  manganese  in  it  by  evaporating  a  weighed 
amount  of  the  solution  to  dryness,  heating  to  dull  redness  and 
weighing  as  manganese  sulphate,  which,  multiplied  by  0.36409 
gives  the  amount  of  manganese.  5  grams  of  "C.  P."  man- 
ganese sulphate  dissolved  in  500  cc.  of  water  and  filtered  will 
give  a  solution  containing  about  0.0035  gram  of  manganese  to 
the  gram  of  solution.  Weigh  i  to  3  grams  of  the  solution  in  a 
crucible,  transfer  to  a  200  cc.  flask,  using  50  cc.  of  nitric  acid 
(sp.  gr.  1.135),  cool,  add  0.5  to  i  gram  bismuthate  and  allow  it 
to  stand  for  3  or  4  minutes,  shaking  at  intervals.  Add  50  cc. 
of  3  per  cent,  nitric  acid  and  filter  through  the  asbestos  filter 
and  wash  with  50  or  60  cc.  of  the  same  acid.  Run  25  cc.  of  the 
ferrous  sulphate  solution  into  the  flask  from  the  pipette  and 
titrate  with  the  permanganate  solution  to  a  faint  pink.  Subtract 
the  number  of  cubic  centimeters  of  the  permanganate  solution 
obtained  from  the  value  of  the  25  cc.  of  ferrous  sulphate  solution 
in  permanganate  and  the  result  is  the  number  of  cubic  centi- 
meters of  the  permanganate  corresponding  to  the  manganese  in 
the  manganese  sulphate  solution  used.  Divide  the  weight  of 
the  manganese  in  the  manganese  sulphate  used  by  the  number 
of  cubic  centimeters  of  permanganate,  and  the  result  is  the  value 
of  i  cc.  of  permanganate  in  manganese. 

Example.  —  One  gram  manganese  sulphate  solution  contains 
0.003562  gram  manganese;  2.0372  grams  manganese  sulphate 
solution  equals  0.0072565  gram  manganese;  25  cc.  ferrous  sul- 
phate solution  equals  24.5  cc.  permanganate  solution;  2.0372 
grams  manganese  sulphate,  after  oxidation  and  addition  of  25 


176  TECHNICAL    METHODS  OF  ORE   ANALYSIS. 

cc.  ferrous  sulphate  solution,  require  3.6  c:.  permanganate  solu- 
tion; 24.5  cc.  —  3.6  cc.  =  20.9  cc.;  0.0072565  divided  by  20.9  = 
0.0003472,  or  i  cc.  of  permanganate  equals  0.0203472  gram  of 
manganese.  If  then  i  gram  of  steel,  after  oxidation  and  addition 
of  25  cc.  ferrous  sulphate  solution,  requires  6.2  cc.  permanganate 
solution  to  give  the  pink  color,  24.5  —  6.2  =  18.3  X  0.0003472  = 
0.006354  gram,  or  the  sample  contains  0.635  Per  cent,  manganese. 

Notes  and  Precautions. 

The  delicacy  of  the  reaction  of  manganese  in  nitric  acid 
solution  with  sodium  bismuth  ate  is  extraordinary.  0.000005 
gram  of  manganese  gave  an  appreciable  color  in  50  cc.  of 
solution. 

When  the  proper  precautions  are  observed,  this  method  for 
materials  containing  small  amounts  of  manganese,  say  up  to  2 
.per  cent.,  is  more  accurate  than  any  other  method,  volumetric  or 
gravimetric,  that  I  have  ever  used. 

As  will  be  seen  in  the  description  of  the  various  methods  of 
solution,  the  use  of  hydrochloric  acid  has  been  avoided  because 
the  presence  of  even  traces  of  this  reagent  is  fatal  to  the  accuracy 
of  the  method.  Where  it  is  impossible  to  avoid  its  use  and  its 
presence  is  suspected  in  the  final  nitric  acid  solution,  the  addition 
of  a  drop  or  two  of  silver  nitrate  will  overcome  the  difficulty,  but 
the  filter  must  be  rejected  after  using  it  for  filtering  a  solution 
so  treated. 

Any  form  of  asbestos  filtering  tube  may  be  used  for  filtering 
off  the  bismuthate,  but  the  perforated  cone  with  bell  jar,  shown 
in  Fig.  17,  is  the  most  satisfactory,  because  it  has  the  largest  area 
of  filtering  surface.  One  filter  may  be  used  for  fifty  or  more 
determinations  and  the  time  occupied  in  filtering  and  washing 
one  determination  is  only  from  one  minute  and  a  half  to  three 


MANGANESE.  177 

minutes.  The  filtrate  must  ,be  perfectly  clear,  for  the  least 
particle  of  bismuthate  carried  through  will  vitiate  the  result  by 
reacting  with  the  excess  of  ferrous  sulphate.  As  soon  as  the 
filtration  and  washing  are  completed,  the  ferrous  sulphate  should 
be  added  and  the  excess  titrated  with  the  permanganate  solution, 
as  the  permanganic  acid  gradually  decomposes  on  standing  and 
the  warmer  the  solution  the  more  rapid  is  the  decomposition. 
At  a  temperature  of  5°  C.  the  solution  will  remain  unaltered  for 
several  hours,  but  at  40°  C.  fifteen  minutes  will  show  an  appre- 
ciable change.  The  larger  the  amount  of  manganese  the  more 
rapid  the  change.  It  is  especially  important  not  to  allow  the 
solution  to  stand  after  adding  the  ferrous  sulphate,  as  the  excess 
of  this  reagent  reacts  with  the  nitric  acid  in  a  few  minutes  and 
the  formation  of  the  smallest  amount  of  nitrous  oxide  is  fatal  to 
the  accuracy  of  the  determination.  For  this  reason  it  is  impor- 
tant to  boil  off  every  trace  of  nitrous  oxide  when  in  the  earlier 
part  of  the  operation  sulphurous  acid  or  other  deoxidizing  agent 
is  added. 

When  working  with  steels  of  unknown  manganese  content, 
it  may  often  happen  that  25  cc.  of  ferrous  sulphate  solution  are 
insufficient  to  entirely  reduce  the  permanganic  acid,  in  which 
case  an  additional  amount  of  ferrous  sulphate  must  be  added 
and  the  pipette  shown  in  Fig.  18  has  been  arranged  to  meet  this 
contingency.  It  will  be  noticed  that  the  solution  of  permanganic 
acid  upon  the  addition  of  an  insufficient  amount  of  ferrous  sul- 
phate does  not  necessarily  retain  its  pink  or  purple  color,  but 
usually  changes  to  a  dirty  brown.  When  this  occurs,  the  lower 
part  of  the  pipette  may  be  emptied  directly  into  the  flask  and  the 
value  of  the  two  parts  taken  as  the  amount  from  which  the 
number  of  cubic  centimeters  of  permanganate  corresponding  to 
the  excess  of  ferrous  sulphate  must  be  subtracted.  When  the 
sample  is  low  in  manganese,  the  10  cc.  portion  of  the  pipette  alone 


178  TECHNICAL    METHODS  OF    ORE  ANALYSIS. 

may  be  used,  so  that  the  arrangement  allows  a  great  deal  of 
variation  in  the  manganese  content  of  the  samples  worked  on. 

There  is  no  advantage  in  using  permanganate  solutions  differ- 
ing in  strength  from  the  one  given  above,  but  the  strength  of 
the  ferrous  sulphate  solution  may  be  changed  to  meet  special 
cases. 


CHAPTER  XIX. 

MERCURY. 

i.  Wet  Method. — Applicable  to  cinnabar  ores  not  contain- 
ing appreciable  amounts  of  other  reducible  metallic  compounds. 

Treat  1-5  grams  of  the  ore,  according  to  its  supposed  rich- 
ness, in  a  covered  porcelain  dish  with  sufficient  aqua  regia  to 
decompose  it.  Heat  gently  until  decomposition  is  complete,  and 
then  remove  and  wash  the  cover  and  evaporate  the  solution  to 
dryness  on  a  water-bath.  Take  up  the  residue  in  strong  hydro- 
chloric acid  and  again  evaporate  to  dryness  to  expel  all  of  the 
nitric  acid.  Again  dissolve  in  hydrochloric  acid,  dilute  suffi- 
ciently and  filter.  To  the  nitrate  add  an  excess  of  a  clear  stannous 
chloride  solution  containing  an  excess  of  acid  (which  may  be 
made  by  dissolving  tin  in  an  excess  of  hydrochloric  acid),  and 
boil  the  mixture  for  a  short  time.  The  mercuric  chloride  is 
reduced  to  finely  divided  metallic  mercury.  Allow  the  precipitate 
to  settle  completely  and  then  decant  the  clear  liquid  carefully. 
Unite  the  precipitate  into  one  globule  by  heating  it  with  a  little 
moderately  dilute  hydrochloric  acid  mixed  with  a  few  drops  of 
stannous  chloride.  Wash  the  mercury  by  decantation,  first 
with  water  slightly  acidified  with  hydrochloric  acid,  and  then 
with  pure  water,  and  then  transfer  it  to  a  weighed  porcelain 
crucible.  Absorb  as  much  of  the  adhering  water  as  possible 

179 


l8o  TECHNICAL   METHODS  OF   ORE  ANALYSIS. 

with  filter-paper  and  then  place  the  crucible  in  a  desiccator  over 
sulphuric  acid.  When  perfectly  dry  weigh  as  metallic  mercury. 

The  results  obtained  by  this  method  are  certain  to  be  some- 
what low  owing  to  the  impossibility  of  evaporating  the  hydro- 
chloric acid  solutions  to  dryness,  in  driving  off  the  nitric  acid, 
without  volatilization  of  some  mercuric  chloride  with  the  escaping 
steam.  As  a  technical  method,  however,  for  low-grade  cinnabar 
ores  it  answers  very  well. 

2.  Dry  Method.  Applicable  to  all  ores. — Prepare  a  combus- 
tion-tube about  1 8  or  20  inches  long  and  sealed  at  one  end. 
Place  in  the  closed  end  a  column  of  crushed  magnesite  about 
4  inches  long,  then  add  a  section  of  about  2  inches  of  freshly 
ignited  caustic  lime,  then  about  4  inches  of  an  intimate  mixture 
of  a  weighed  portion  of  the  ore  with  an  excess  of  caustic  lime, 
rinsing  out  the  mortar  with  a  little  lime  and  adding  this  also, 
and  then  about  2  inches  of  caustic  lime.  Finally,  insert  against 
the  whole  a  loose  plug  of  asbestos  about  2  inches  long.  Now 
draw  out  the  end  of  the  tube  to  a  narrow  opening  and  bend  it 
at  right  angles.  Tap  the  tube  horizontally  on  the  table,  gently, 
so  as  to  leave  a  free  passage  for  gases  throughout  its  length. 
Place  the  tube  in  a  combustion  furnace  and  arrange  a  small 
flask  party  filled  with  water  so  that  the  point  of  the  tube  just 
touches  the  water,  which  thus  closes  it.  Now  proceed  to  heat 
the  tube,  beginning  at  the  end  containing  the  asbestos  and  grad- 
ually approaching  the  other  end,  until  the  tube  is  red-hot  through- 
out the  entire  portion  in  the  furnace.  The  carbon  dioxide  evolved 
from  the  magnesite  serves  to  sweep  out  the  last  traces  of  mercury 
vapor  into  the  water.  While  the  tube  is  still  hot  cut  off  the  point 
above  the  flask  and  rinse  any  condensed  mercury  into  the  water. 
Agitate  the  flask  so  as  to  collect  the  mercury  into  one  globule, 
and,  after  allowing  to  stand  and  settle  some  time,  decant  off 
the  perfectly  clear  water  and  transfer  the  mercury  to  a  weighed 


MERCURY.  181 

porcelain  crucible.  Remove  as  much  of  the  adhering  water  as 
possible  with  filter-paper  and  then  dry  the  mercury  to  constant 
weight  over  sulphuric  acid  in  a  desiccator.  It  must  not  be  heated. 

3.  Eschka's   Method.*    Particularly   applicable   to   low-grade 
ores. — Mix  from  0.2  to  2  grams  of  the  ore  with  from  i  to  4  grams 
of  iron  filings  in  a  porcelain  crucible  of  suitable  size.     Prepare 
a  dish-shaped  cover  of  thin  sheet  gold  for  the  crucible,  that  may 
be  kept  cool  by  being  filled  with  water.     To  prevent  any  mercury 
from  escaping,  the  cover  should  be  large  enough  to  project  some- 
what over  the  edge  of  the  crucible.     Place  the  crucible  in  a  ring- 
stand,  put  on  the  weighed  cover  and  nearly  fill  it  with  water. 
Carefully  heat  the  lower  part  of  the  crucible  with  a  Bunsen  burner, 
but  keep  the  upper  part  cool.     A  ring  of  thin  asbestos  board 
fitted  around  the  crucible  at  the  proper  height  will  assist  materially 
in  preventing  the  top  from  getting  overheated.      Add  cold  water 
to  the  cover  from  time  to  time.     It  will  require  from  10  to  30 
minutes  to  distill  off  the  mercury.     When  the  operation  is  con- 
sidered ended  remove  the  gold  cover,  dry  carefully  without  heat- 
ing and  weigh.     The  increase  over  the  original  weight  represents 
the  mercury,     A   silver  cover  appears  to  answer  practically  as 
well  as  one  of  gold 

4.  Krieckhaus'  Volumetric  Method. f — Weigh  2  grams  of  the 
ore   into   a    i5o-cc.    beaker.     Add    2  cc.    of   strong   nitric   acid 
and  10  cc.  of  strong  hydrochloric  acid.     Measure  the  nitric  acid 
first  and  then  measure  the  hydrochloric  without  washing  the 
glass.     This  ensures  getting  all  of  the  nitric  acid,  which  is  essen- 
tial, although  an  excess  must  be  avoided. 

Allow  to  stand  cold  for  an  hour  or  more,  when  the  mercury 

*  Zeit.  f.  anal.  Chem.,  Vol.  n,  p.  344. 

f  Kindly  furnished  by  Mr.  Leon  L.  Krieckhaus.  The  description  was  received 
too  late  for  experimental  tests  in  my  laboratory,  but  the  results  sent  by  Mr.  Krieck- 
haus check  closely  with  those  he  obtained  by  Eschka's  method. 


1 82  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

will  all  be  in  solution;  or,  to  save  time,  heat  slightly  but  not  to 
boiling.  Now  dilute  with  10-15  cc.  of  water,  heat  nearly  to  boil- 
ing and  filter  into  a  3OO-cc.  Erlenmeyer  flask,  washing  with  hot 
water.  To  the  filtrate,  which  contains  the  mercury  (and  need 
not  be  much  over  100  cc.  in  volume),  add  60  cc.  of  stannous 
chloride  solution  (prepared  as  described  below),  cork  the  flask 
and  allow  to  stand,  tilted  at  an  angle  of  about  45°,  until  the 
mercury  has  all  settled  and  the  liquid  is  clear.  The  settling 
takes  about  two  hours. 

Decant  the  liquid  and  then  fill  the  flask  about  two-thirds 
full  with  cold  water,  slightly  acidulated  with  sulphuric  acid  to 
prevent  the  separation  of  basic  tin  salts.  Again  allow  to  settle 
with  the  flask  tilted  as  before.  If  any  mercury  floats,  a  jet  of 
water  will  cause  it  to  settle.  In  about  10  minutes  decant  the 
clear  liquid  as  completely  as  possible.  Dissolve  the  precipitated 
mercury  in  2  or  3  cc.  of  strong  nitric  acid,  warming  gently  to 
ensure  complete  solution  and  oxidation  to  mercuric  nitrate. 

Add  about  75  cc.  of  cold  water  and  a  few  cubic  centimeters 
of  a  solution  of  ferric  nitrate,  as  indicator  (or  ferric  ammonium 
alum  slightly  acidulated  with  nitric  acid),  and  titrate  cold  with 
standard  potassium  thiocyanate  solution  to  the  usual  red  tinge. 

5.  If  the  potassium  thiocyanate  solution  contains  9.722  grams 
of  the  salt  per  liter,  i  cc.  will  equal  o.oi  gram  of  mercury,  or 
0.5  per  cent,  on  the  basis  of  2  grams  of  ore  taken  for  assay. 
It  is  best  to  standardize  it  with  pure  silver  or  silver  nitrate,  as 
described   in   vi,   7.     The  silver  value  of    i  cc.   multiplied   by 
0.9265  will  give  the  mercury  value. 

Prepare  the  stannous  chloride  solution  by  mixing  50  grams 
of  the  salt,  50  cc.  of  strong  hydrochloric  acid  and  150  cc.  of 
water,  and  boiling  with  a  stick  of  metallic  tin  until  clear.  Keep 
a  stick  of  tin  in  the  bottle. 

6.  Notes  by  Mr.  Krieckhaus. — If  lead  is  present  in  an  ore,  it 


MERCURY.  183 

can  probably  be  largely  removed  by  adding  a  little  sulphuric  acid 
before  filtering  off  the  gangue.  If  any  remains  in  solution  and 
comes  down  as  chloride  with  the  mercury,  the  chlorine  it  carries 
will  interfere,  but  the  lead  chloride  could  probably  be  washed 
out  of  the  mercury  with  hot  water.  Stannous  chloride  precipi- 
tates copper  as  cuprous  chloride,  but  this  may  be  easily  removed 
with  dilute  ammonia. 

In  order  that  the  mercury  shall  settle  well  it  is  best  to  have 
the  solution  cold  and  the  tin  solution  quite  strongly  acid,  but  not 
saturated  with  stannous  chloride.  Add  only  i  or  2  cc.  of  the  tin 
solution  at  first  and  agitate  the  flask.  This  will  cause  a  precipi- 
tation of  mercurous  chloride.  Then  add  the  remainder  of  the 
tin  solution  and  allow  to  stand  as  above  described.  Under  these 
conditions  the  mercury  will  settle  clear  in  an  hour  or  two.  If  the 
liquid  is  hot  or  the  tin  solution  too  strong,  the  mercury  is  so  finely 
divided  that  it  is  slow  to  settle  and  difficult  to  wash  without  loss. 

7.  Seamen's  Volumetric  Method.* — Weigh  0.5  gram  of  the 
finely  ground  ore  into  an  Erlenmeyer  flask  of  125  cc.  capacity. 
Add  5  cc.  of  strong  hydrochloric  acid  and  allow  it  to  act  for 
about  ten  minutes  at  a  temperature  of  about  40°  C,  then  add 
3  cc.  of  strong  nitric  acid  and  allow  the  action  to  continue  for 
about  ten  minutes  longer.  The  mercury  should  now  all  be  in 
solution.  Now  if  lead  be  present,  add  5  cc.  of  strong  sulphuric 
acid;  it  may  be  omitted  otherwise.  Dilute  with  15  cc.  of  water 
and  then  add  ammonia  cautiously  until  the  liquid  is  slightly 
alkaline.  Bismuth,  if  present,  will  precipitate.  Acidify  faintly 
with  nitric  acid,  filter,  receiving  the  filtrate  in  a  beaker,  and 
wash  thoroughly. 

Add  to  the  filtrate  i  cc.  of  strong  nitric  acid  that  has  been 
made  brownish  in  color  by  exposure  to  the  light,  and  titrate 

*  Manual  for  Assayers  and  Chemists,  p.  112. 


1 84  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

with  a  standard  solution  of  potassium  iodide  until  a  drop  of 
the  liquid  brought  into  contact  with  a  drop  of  starch  liquor, 
on  a  spot-plate,  shows  a  faint  bluish  tinge.  It  is  a  good  plan 
to  set  aside  about  one-third  of  the  mercury  solution  and  add  it 
in  portions  as  the  end-point  is  successively  passed,  finally  rinsing 
in  the  last  portion  and  titrating  to  the  end-point  very  carefully. 

Deduct  0.5  cc.  from  the  burette  reading  and  multiply  the 
remaining  cubic  centimeters  used  by  the  percentage  value  of 

1  cc.  in  mercury  to  obtain  the  percentage  in  the  ore. 

The  standard  potassium  iodide  solution  should  contain  8.3 
grams  of  the  salt  per  liter.  Standardize  against  pure  mercuric 
chloride.  Dissolve  a  weighed  amount  of  the  salt  in  water,  add 

2  cc.  of  the  discolored  nitric  acid  and  titrate  as  above,     i  cc.  of 
the  standard  solution  will  be  found  equivalent  to  about  0.005 
gram  of  mercury,  or  about  i  per  cent,  on  the  basis  of  0.5  gram 
of  ore  taken  for  assay. 

The  precipitate  of  red  mercuric  iodide  which  forms  during 
the  titration  may  not  appear  if  the  amount  of  mercury  present 
is  very  small,  but  this  failure  to  precipitate  does  not  appear  to 
affect  the  result. 

Iron,  copper,  bismuth,  antimony  and  arsenic,  when  added 
separately  to  the  ore,  did  not  influence  the  results  in  Seamon's 
tests.  Silver  interferes.  Duplicate  results  should  check  within 
0.1-0.2  of  one  per  cent 


CHAPTER  XX. 

MOLYBDENUM. 

i.  Method  for  Ores. — Fuse  i  gram  of  the  ore  in  a  platinum 
dish  or  crucible  with  4  grams  of  sodium  carbonate  and  0.5  gram 
of  potassium  nitrate.  Cool  and  extract  the  melt  with  hot  water. 
If  the  solution  shows  any  color  due  to  manganese  add  a  little 
alcohol  and  warm  so  as  to  effect  its  reduction  and  precipitation. 
Filter,  washing  with  hot  water.  Nearly,  but  not  quite,  neutralize 
the  nitrate  with  nitric  acid.  The  amount  to  use  should  be  ascer- 
tained by  a  blank  test  on  exactly  4  grams  of  sodium  carbonate. 
Evaporate  the  solution  to  approximate  dryness,  dilute,  filter  and 
add  to  the  cold  alkaline  solution  a  solution  of  mercurous  nitrate 
until  it  ceases  to  effect  a  further  precipitation.  The  precipitate  con- 
sists of  mercurous  molybdate>  besides  mercurous  carbonate  pro 
duced  by  the  slight  excess  of  alkali  carbonate  left  in  the  solution. 
Any  chromium,  vanadium,  tungsten,  phosphorus,  or  arsenic 
present  will  also  be  precipitated.  The  mercurous  carbonate 
serves  to  neutralize  the  free  nitric  acid  always  present  in  the  mer- 
curous nitrate.  If  the  alkalinity  was  too  great,  as  shown  by  the 
precipitate  becoming  unduly  large  and  still  increasing  as  mer- 
curous nitrate  is  added,  add  nitric  acid  drop  by  drop  until  an 
added  drop  of  mercurous  nitrate  produces  no  cloud.  Heat  the 
liquid  to  boiling  and  filter  off  the  black  precipitate.  Wash  with 
a  dilute  solution  of  mercurous  nitrate.  Dry  the  filter  and  pre- 

185 


i86  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

cipitate  and  transfer  the  latter  as  completely  as  possible  to  a 
watch-glass.  Dissolve  the  precipitate  still  remaining  on  the 
filter  in  hot  dilute  nitric  acid  and  receive  the  solution  in  a  large 
weighed  porcelain  crucible.  Evaporate  the  solution  to  dryness 
on  a  water-bath  and  then  add  the  main  portion  of  the  precipitate. 
Heat,  without  melting,  over  a  very  low  flame  until  the  mercury 
is  completely  volatilized.  Cool  and  weigh  as  MoO3.  Multiply 
this  weight  by  0.6667  to  obtain  the  weight  of  the  molybdenum. 

2.  In  case  the  ore  contained  chromium,  vanadium,  tungsten, 
phosphorus,  or  arsenic  in  appreciable  amount,  the  ignited  MoO3 
must  be  further  treated  as  follows: 

To  avoid  transference  the  ignition  should  be  made  in  a 
small  platinum  dish.  Fuse  with  a  very  little  sodium  carbonate 
and  leach  the  residue  with  hot  water  and  filter.  To  the  filtrate 
add  sulphuric  acid  in  slight  excess  and  transfer  to  a  small  pressure 
flask.  Pass  in  hydrogen  sulphide  to  saturation  in  the  cold, 
then  close  the  flask,  heat  on  the  water-bath  until  the  precipitate 
has  completely  settled,  allow  to  cool  and  filter.  Wash  first  with 
very  dilute  sulphuric  acid  and  then  with  alcohol  until  the  acid 
is  all  removed.  The  precipitate  consists  of  molybdenum  and 
arsenic  sulphides  and  sometimes  contains  also  traces  of  platinum 
from  the  dish.  Place  the  moist  precipitate  and  filter  in  a  large 
weighed  porcelain  crucible,  dry  thoroughly  on  a  water-bath, 
then  cover  the  crucible  and  heat  very  carefully  over  a  small  flame 
until  volatile  hydrocarbons  are  expelled.  Now  remove  the 
cover  and  burn  the  carbon  from  the  sides  of  the  crucible  at  as 
low  a  temperature  as  possible.  Finally,  increase  the  heat  grad- 
ually until  the  molybdenum  sulphide  is  all  changed  to  oxide, 
i.e.,  until  no  more  sulphur  dioxide  is  evolved.  Cool,  add  a  little 
mercuric  oxide  suspended  in  water,  stir  the  mixture  well,  evaporate 
to  dryness  on  the  water-bath  and  then  expel  the  mercuric  oxide 
by  gentle  ignition  and  weigh  the  residue,  after  cooling,  as 


MOLYBDENUM.  187 

The  mercuric  oxide  effects  the  oxidation  of  any  unburned  particles 
of  carbon  from  the  filter-paper. 

3.  If   the   color   of   the  sulphide  precipitate  showed  arsenic 
to  be  absent  the  last  result  may  be  accepted  as  correct.    When 
arsenic  is  present,  or  in  case  of  doubt,  fuse  the  last  residue  in  the 
crucible  with  a  little  mixed  sodium  and  potassium  carbonates  at 
as  low  a  temperature  as  possible  and  leach  the  melt  with  hot 
water.      Filter,  add  one-third   its  volume  of  strong  ammonia  to 
the  filtrate  and  then  about  20  cc.-of  "magnesia  mixture"  (p.  213). 
Add  the  latter  drop  by  drop  with  constant  stirring.     Allow  to 
stand,  covered,  12  hours  in  the  cold  and  then  filter.     Wash  well 
with  2\  per  cent,  ammonia.     Acidify  the  filtrate  with  dilute  sul- 
phuric acid,  transfer  to  a  pressure  flask  and  repeat  the  operations 
described  in  2. 

4.  The  presence  of  molybdenum  may  be  shown  in  the  final 
residue  as  follows:  Heat  the  residue,  or  a  little  of  it,  in  porcelain, 
with  a  single  drop  of  strong  sulphuric  acid  until  the  latter  is 
nearly  volatilized.     On  cooling,  a  beautiful  blue  color  is  proof 
of  the  presence  of  molybdenum. 


CHAPTER   XXI. 

NICKEL  AND  COBALT. 

NICKEL  and  cobalt  require  the  same  procedure  at  the  outset, 
and  when  a  separate  determination  of  either  or  both  is  required 
it  is  made  after  the  elements  or  their  compounds  have  been 
separated  together  from  interfering  substances. 

i.  Method  for  Ores,  etc. — To  0.5  gram  of  the  ore  in  an  8-oz. 
flask  add  about  10  cc.  of  strong  nitric  acid  and  boil  until  the  red 
fumes  have  about  ceased  coming  off,  or  until  the  acid  is  about 
half  gone.  Then  add  about  5  grams  of  fine  crystallized  potassium 
chlorate  and  5  cc.  more  nitric  acid.  Boil  to  complete  dryness, 
but  avoid  overheating  the  residue,  It  is  best  to  manipulate  the 
flask  over  a  free  flame  to  save  time  and  avoid  loss  by  bumpingu 
Towards  the  last,  spread  the  pasty  mass  around  on  the  inside 
of  the  flask  so  as  to  form  a  thin  layer.  When  completely  dry, 
cool  and  add  35  cc.  of  strong  ammonia  water  and  warm  gently 
until  the  residue  is  disintegrated  as  thoroughly  as  possible.  Now 
add  about  15  cc.  of  strong  bromine  water  and  heat  a  while  longer 
to  precipitate  any  manganese  in  solution.  Filter,  washing  with 
hot  water.  Rinse  the  residue  on  the  filter  back  into  the  flask 
again,  place  the  latter  under  the  funnel  and  pour  a  little  hot, 
dilute  (1:2)  hydrochloric  acid  through  the  filter  to  dissolve  all 
remaining  residue  and  wash  with  water.  Boil  the  contents  of 
the  flask  to  completely  dissolve  the  soluble  portion  of  the  residue, 

188 


NICKEL  AND  COBALT.  189 

dilute  somewhat,  add  15  cc.  of  strong  bromine  water  and  then 
ammonia  in  excess.  Boil  for  a  short  time  and  then  filter  and 
wash  with  hot  water  thoroughly. 

2.  Unite  the  two  filtrates,  which  now  contain  practically  all 
the  nickel  and  cobalt,*  in  a  large  casserole,  and  boil  off  most  of 
the  excess  of  ammonia.  Make  just  acid  with  hydrochloric  acid 
and  then  add  5  cc.  in  excess.  Again  heat  to  boiling  and  boil  for 
a  few  minutes  to  decompose  chlorates,  etc.  Dilute,  if  necessary, 
to  about  250  cc.  with  hot  water  and  pass  in  hydrogen  sulphide 
until  cold.  Filter  off  the  sulphides  of  copper,  lead,  etc.,  and 
wash  with  dilute  hydrogen  sulphide  water.  Receive  the  filtrate 
in  a  large  casserole  (5-  or  6-inch.) 

3.  Boil  the  solution  until  the  hydrogen  sulphide  is  com- 
pletely expelled  and  then  add  a  solution  of  pure  potassium 
hydroxide  in  excess  and  keep  at  nearly  boiling  temperature  for 
some  time.  The  color  of  the  precipitate  thus  obtained  will 
indicate  the  presence  or  absence  of  cobalt.  If  of  a  pure  apple- 
green  color,  no  cobalt,  or  only  an  insignificant  amount  is  present. 
The  cobalt  precipitate  is  at  first  blue  but  soon  changes  to  black, 
by  contact  of  the  liquid  with  the  air,  and  thus  the  comparative 
amount  of  cobalt  present  can  be  judged  by  the  degree  of  discolora- 
tion. Filter  the  precipitate  and  wash  with  hot  water. 

4.  If  the  precipitate  is  of  a  pure  apple-green  color  and  very 
small  in  amount,  with  no  evidence  of  the  presence  of  alkaline- 
earthy  carbonates,  it  will  often  suffice,  after  washing  thoroughly, 
to.  ignite  and  weigh  it  as  NiO.  Multiply  by  0.7858  to  obtain 
the  weight  of  the  nickel.  If  simply  discolored  with  cobaltic 
hydroxide,  but  otherwise  apparently  pure  and  small  in  amount, 


*  If  considered  desirable,  the  iron  precipitate  may  be  again  redissolved  and  a 
basic  acetate  separation  made,  the  filtrate  from  this  being  sufficiently  evaporated 
and  added  to  the  other  filtrates.  In  technical  work  I  have  rarely  found  this  neces- 
sary. 


I po  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

it  may  be  sufficient  to  ignite  and  weigh  as  NiO  and  report,  ofter 
calculation,  as  combined  nickel  and  cobalt. 

5.  If  the  amount  of  precipitate  is  large  and  apparently  free 
from  cobalt,  it  may  still  contain  zinc,  if  the  latter  was  present 
in   the  original   substance,   and   alkaline-earth    carbonates,   pre- 
cipice ted  by  the  carbonate  in  the  caustic  alkali  used.     In  such  a 
case  it  may  sometimes  suffice  to  redissolve  and  make  a  second 
precipitation  as  follows:    Dissolve  the  precipitate  on  the  filter 
in  warm  dilute  (1:3)  hydrochloric  acid  and  receive  the  filtrate 
in  the  large  casserole  previously  used.     Dilute  the  solution  suf- 
ficiently, heat  to  boiling,  and  add  an  excess  of  pure  potassium 
hydroxide  and  some  bromine  water.     The  nickel  is  precipitated 
as    brownish-black    nickelic    hydroxide,  Ni(OH)3.      When    the 
operation  is  complete  filter  off  the  precipitate,  washing  with  hot 
water,   first  by  decantation   and   then   on   the  filter.     Dry  and 
ignite  the  residue  and  weigh  as  NiO.     If  the  impurities  present 
in  the  first  precipitate  were  not  large  in  amount  they  will  be 
mostly    eliminated    by    the    second    precipitation.     The    ignited 
NiO  will  contain  no  alkali,  but  usually  has  traces  of  silica. 

6.  If   it  is  desired  to  determine  the  amount  of  silica  mixed 
with  the  NiO,  dissolve  the  latter  in  the  crucible  in  hydrochloric 
acid,  evaporate  to  complete  dryness,  moisten  with  strong  hydro- 
chloric acid  and  then  take  up  with  hot  water.     Filter  through  a 
small  filter  and  wash  with   hot  water.     Ignite  the  moist  filter 
and  residue  and  weigh  as  SiO2. 

The  above  are  given  simply  as  approximate  methods  that 
will  frequently  serve  where  the  ore  is  fairly  free  from  interfering 
impurities  and  where  any  cobalt  present  may  be  reported  as 
nickel. 

7.  For  more  exact  results,  including  the  separation  of  nickel 
and  cobalt,  proceed  as  follows:    Begin  as  before  (i)  and  con- 
tinue   as    described,    omitting,    however,    the    use    of   bromine, 


NICKEL  AND   COBALT.  191 

un  til  the  filtrate  from  the  hydrogen  sulphide  precipitate  is  obtained. 

Boil  this  filtrate  until  the  hydrogen  sulphide  is  completely  expelled 
and  then  add  ammonia  in  slight  excess.  Now  acidify  slightly 
with  acetic  acid,  add  i  or  2  grams  of  ammonium  acetate,  heat 
to  7o°-8o°  C.  and  saturate  with  hydrogen  sulphide.  The  nickel 
and  cobalt  are  precipitated  as  sulphides.  Filter,  washing  with 
hot  water.  The  filtrate  may  still  contain  small  amounts  of 
nickel  and  cobalt.  Concentrate  it  and  add  some  colorless  am- 
monium sulphide.  Make  slightly  acid  with  acetic  acid,  warm 
and  filter.  If  a  precipitate  is  obtained,  collect  it  on  a  separate 
filter.  Repeat  this  testing  of  the  filtrate  until  no  further  pre- 
cipitation is  produced. 

8.  Wash  the  precipitated  sulphides  from  the  filters,  as  com- 
pletely as  possible,  into  a  small  porcelain  dish  or  casserole. 
Dry  and  burn  the  filters  and  add  the  ash  also.  Dissolve  the 
whole  in  hydrochloric  acid  and  a  little  nitric  acid.  The  solution 
now  contains  nickel,  cobalt,  and  possibly  zinc.  To  remove  the 
latter,  evaporate  to  small  volume,  add  2  or  3  grams  of  pure  finely 
crystallized  ammonium  chloride,*  evaporate  to  dryness  on  a 
water-bath  and  then  heat  carefully  until  all  the  ammonium 
chloride  is  expelled.  The  zinc  is  driven  off  at  the  same  time. 
When  cool,  dissolve  the  residue  in  nitrohydrochloric  acid  and 
expel  the  excess  of  acid  by  evaporating  nearly  to  dryness.  Dilute 
sufficiently,  heat  to  boiling,  add  an  excess  of  pure  potassium 
hydroxide  and  some  bromine  water.  Filter  and  wash  thoroughly 
with  hot  water,  first  by  decantation,  then  on  the  filter.  Dry  and 
ignite.  If  only  nickel  is  present,  or  if  nickel  and  cobalt  are  to  be 
determined  together,  the  residue  may  be  weighed  as  NiO  and 
the  metal  reported,  after  calculation  (factor,  0.7858)  as  Ni,  or, 
Ni  +  Co.  Determine  and  deduct  silica  if  desired  (6). 

*  Fresenius.     Zejt.  fttr.  Anal.  Chem.     Schaeffer,  Am.  Chem.,  IV,  289.     Fres- 
enius  prescribes  5  grams  ammonium  chloride  for  every  0.2  gram  ZnO. 


192  TECHNICAL   METHODS  OF  ORE   ANALYSIS. 

9.  When  the  metals  are  to  be  determined  separately,*  pre- 
cipitate the  nickel  and  cobalt  as  hydroxides  from  the  last  solution 
above,  without  the  addition  of  bromine.  Heat  nearly  to  boiling 
for  some  time  and  then  filter  and  wash  only  once  or  twice  with 
hot  water.  The  two  metals  may  now  be  separated  by  Liebig's 
mercuric  oxide  method,  as  modified  by  Wohler.  Wash  the 
hydroxides  from  the  filter  into  a  large  casserole,  then  place  the 
latter  under  the  funnel  and  pour  a  saturated  solution  of  potassium 
cyanide  over  the  filter  to  dissolve  whatever  precipitate  still  remains. 
Wash  the  filter  with  hot  water  and  warm  the  filtrate  and  mixed 
hydroxides  until  solution  is  complete,  adding  more  potassium 
cyanide  if  required  but  avoiding  an  unnecessary  excess.  Heat 
the  solution  for  at  least  one  hour  on  the  water-bath,  to  convert 
the  cobalt  compound  into  potassium  cobalticyanide.  Now  add 
to  the  hot  solution  an  excess  of  finely  pulverized  red  mercuric 
oxide  and  boil  the  mixture  for  an  hour.  The  nickel  is  pre- 
cipitated as  nickelous  hydroxide  according  to  the  reaction 

K2Ni(CN)4+  2HgO  +  2H2O  =Ni(OH)2  +  2KOH  +  2Hg(CN)2. 

Dilute  somewhat  with  hot  water,  if  necessary,  filter,  wash  with 
hot  water,  dry,  ignite  and  weigh  as  NiO.  The  ignition  should  be 
performed  under  a  hood  to  avoid  the  poisonous  fumes  from  the 
mercury  compound  present.  To  determine  the  impurities  in  the 
NiO  it  may,  after  weighing,  be  transferred  to  a  beaker,  boiled 
with  water,  and  then  filtered,  dried,  ignited,  and  weighed  again. 
Note  .the  loss,  probably  due  to  adhering  alkali.  Now  transfer 
to  a  porcelain  dish,  dissolve  in  nitrohydrochloric  acid,  evaporate 
to  dryness,  moisten  with  strong  hydrochloric  acid  and  then  take 
up  in  hot  water.  Filter  through  a  small  filter,  wash  with  hot 
water  and  then  ignite  the  moist  filter  and  residue  and  weigh  as 
SiO2.  After  deducting  the  weights  of  the  alkali  and  silica  from 

*  Sjc  ii.su  14,  15,  and  18. 


NICKEL  AND   COBALT.  !93 

the  original  weight,  the  balance  may  be  considered  as  the  true 
weight  of  the  NiO  from  which  the  weight  of  the  nickel  may  be 
calculated. 

10.  To  determine  the  cobalt  in  the  filtrate  from  the  nickel, 
carefully  neutralize  with  nitric  acid  so  as  to  leave  the  liquid  very 
slightly  alkaline.     It  must  not  be  acid  or  strongly  alkaline.    Now 
add  a  solution  of  mercurous  nitrate  as  long  as  a  precipitate  ^mer- 
cury    cobalticyanide)    is    produced.     Filter    off    the  precipitate, 
wash,   dry,   and   ignite  with   access   of  air.     Weigh  as   Co3O4. 
Multiply  by  0.7345   to  obtain  the  weight  of  the  cobalt.     The 
degree  of  oxidation  of  the  cobalt  varies  somewhat  with  the  tem- 
perature of  the  ignition,  and  it  is,  therefore,  safer  to  reduce  the 
oxide  by  ignition  in  hydrogen  and  weigh  as  metallic  cobalt. 

11.  Electrolytic    Method.  —  Proceed    as    in    7    and  continue 
as  described  until  the  zinc  has  been  expelled  and  the  residue 
dissolved  in  nitrohydrochloric  acid.      Evaporate    now,   on    the 
water-bath,  completely  to  dryness  and  then  dissolve  the  residue 
in  a  little  dilute  sulphuric  acid.     Transfer  to  the  beaker  in  which 
the  electrolysis  is  to  be  made,  add  about  5  grams  of  ammonium 
sulphate  and  40-60  cc.  of  strong  ammonia  and  dilute  to  about 
125   cc.   with  distilled  water.     The   solution  is  now   ready  fcr 
electrolysis. 

The  electrolytic  apparatus  may  be  the  same  as  described  for 
copper  in  xm,  10.  See  article  ELECTROLYSIS,  p.  10,  for  details 
as  to  arrangement  of  apparatus,  etc. 

12.  Insert   the   electrodes   and   electrolyse   at   room   temper- 
ature with  a  current  density  of  ND 100  =  0.5  — 0.7  amp.  and  an 
electrode  tension  of   2.8-3.3   v°lts.     The  electrolysis  is  usually 
finished  in  from  3   to  4  hours.     To  test  for  its  completion  a 
little  of  the  solution  may  be  removed  with  a  capillary  tube  and 
tested    with   ammonium    sulphide.     If   no   black   precipitate   is 
obtained  the  operation  may  be  considered  ended.     The  solution 


194  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

should  still  be  strongly  ammoniacal.  Having  broken  the  circuit, 
remove  the  cathode,  wash  it  first  with  water  and  then  with  alcohol 
(best,  absolute),  dry  at  about  100°  C.  and  weigh.  The  excess 
over  the  original  weight  represents  the  combined  nickel  and 
cobalt. 

13.  To  separate  the  metals,  dissolve  them  from  the  electrode 
with  a  little  strong  nitric  acid  in  a  small  beaker,  kept  covered  as 
much  as  possible.     Remove  and  wash  the  electrode  and  transfer 
the  solution  to  a  large  casserole  and  evaporate  on  the  water-bath 
completely  to  dryness.     Now  take  up  in  sufficient  strong  potas- 
sium cyanide  solution   to  completely  dissolve   the   residue,  but 
avoiding  any  great  excess,  and  proceed  as  described  in  9.     The 
cobalt  may  either  be  determined  as  there  described  or  estimated 
by  difference. 

14.  Separation  of  Nickel  and  Cobalt  by  Liebig's  Potassium 
Cyanide   Method. — Proceed  as  described  in  7  and  8  until  zinc, 
if   present,   has   been   expelled   and   the   nitrohydrochloric   acid 
solution   of   the   residue   has   been   evaporated   nearly   to   dry- 
ness  to  expel  the  excess  of  acid.     Now  dilute  sufficiently  and 
neutralize  with  pure  potassium  hydroxide,  finally  adding  5  grams 
in  excess;   then  add  pure  potassium  cyanide  until  the  precipitate 
redissolves  and  the  potassium  cyanide  is.  in  slight  excess.     To 
the  warm  solution  add  saturated  bromine  water  with  constant 
stirring  until  the  precipitation  of  the  nickel  as  black  nickelic 
hydroxide   is   complete.     The    solution   must   be    kept    strongly 
alkaline    throughout   the   process.     Finally,    dilute    the   mixture 
with  cold  water  and  filter,  washing  the  precipitate  with  hot  water. 

Dissolve  the  precipitate  in  dilute  sulphuric  acid  and  deter- 
mine the  nickel  electrolytically,  as  described  in  n. 

The  filtrate  contains  the  cobalt  as  potassium  cobalticyanidc. 
Acidify  with  dilute  sulphuric  acid  and  evaporate  as  far  as  pos- 
sible on  the  water-bath,  then  add  a  little  concentrated  sulphuric 
acid  and  heat  the  mixture  over  a  free  flame  until  dense  white 


NICKEL  AND   COBALT.  195 

fumes  are  evolved  and  effervescence  has  ceased.  The  cobalt 
in  the  colorless  potassium  cobalticyanide  is  thus  changed  into 
the  rose-red  sulphate.  Cool,  dilute,  filter  from  any  silica,  and 
determine  the  cobalt  in  the  nitrate  electrolytically,  precisely 
as.  described  for  nickel  (n).  Or,  the  nitrate  may  be  treated 
as  follows:  Heat  to  boiling  in  a  porcelain  casserole  and  pre- 
cipitate the  cobalt  as  black  cobaltic  hydroxide  by  the  addition 
of  potassium  hydroxide  and  bromine  water.  Filter  through  a 
close  filter  (such  as  Schleicher  and  Schull's  No.  589,  blue  band), 
dry  and  ignite.  After  cooling,  extract  with  water  to  remove 
the  small  amount  of  alkali  always  present,  then  dry  the  residue 
and  ignite  in  a  current  of  hydrogen  in  a  Rose  crucible,  finally 
weighing  the  cobalt  as  metal. 

After  weighing,  dissolve  the  metal  in  hydrochloric  acid, 
evaporate  to  dryness,  moisten  the  residue  with  hydrochloric  acid, 
dilute  and  filter  off  the  small  residue  of  silica.  Ignite,  weigh  and 
deduct  this  weight  from  the  previous  one  to  obtain  the  true  weight 
of  the  cobalt. 

15.  Separation  of  Nickel  and  Cobalt  by  the  Nitroso-/?- 
Naphthol  Method. — This  method  is  especially  suitable  for  the 
determination  of  a  small  amount  of  cobalt  in  the  presence  of  a 
large  amount  of  nickel,  since  the  cobalt  precipitate  is  very  volu- 
minous. 

Nitroso-/?-naphthol,  Ci0H6O(NOH),  forms  with  cobalt  the 
compound  Co[CioH6O(NO)]3,  cobalti-nitroso-/?-naphthol,  which 
is  insoluble  in  hydrochloric  acid,  while  the  corresponding  nickel 
compound  is  soluble. 

Proceed  as  described  in  7  and  8  until,  after  the  expulsion 
of  any  zinc,  the  residue  has  been  dissolved  in  nitrohydrochloric 
acid.  Add  a  little  sulphuric  acid  and  heat  over  a  free  flame  to 

*  Illiuske  and  von  Knorre.     Ber.,  18,  699. 


196  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

dense  white  fumes.  Cool,  dilute,  and  add  5  cc.  of  strong  hydro- 
chloric acid.  Now  add  a  freshly  prepared  hot  solution  of  nitroso- 
/?-napthol  in  50  per  cent,  acetic  acid  as  long  as  a  precipitate  is 
produced.  Allow  to  settle  and  then  test  to  see  if  the  precipita- 
tion is  complete.  Digest  at  the  ordinary  temperature  for  a  few 
hours.  Filter  the  precipitate,  which  consists  of  the  cobalt 
compound  mixed  with  considerable  of  the  reagent,  and  wash, 
first  with  cold  water,  then  writh  warm  1 2  per  cent,  hydrochloric 
acid,  thoroughly,  to  remove  all  the  nickel.  Finally,  wash  with 
hot  water  until  free  from  acid. 

Dry  the  precipitate  and  place  it  in  a  weighed  Rose  crucible. 
Add  a  little  pure  crystallized  oxalic  acid  and  ignite.*  Heat  at 
first  very  cautiously  to  avoid  loss,  and  then  with  the  full  power 
of  a  Bunsen  burner.  When  the  carbon  of  the  filter-paper  is  all 
consumed,  reduce  the  cobalt  to  metal  by  heating  in  a  current  of 
hydrogen.  Cool  and  weigh. 

Add  sulphuric  acid  to  the  filtrate,  evaporate  to  small  bulk 
and  then  expel  the  greater  part  of  the  acid  by  heating  over  a 
free  flame. 

The  nickel  may  now  be  determined  as  described  in  5,  or 
electrolytically  (n). 

16.  Sensitive  Test  for  Nickel. f  —  a-Dimethylglyoxime  is  a 
very  sensitive  reagent  for  nickel  in  solution,  and  gives  a  scar- 
let precipitate,  or,  with  traces  of  nickel,  a  yellowish  solution 
from  which  the  red  precipitate  separates  on  cooling.  The 
best  method  of  applying  this  reagent  is  to  remove  the  excess 
of  acid  from  the  solution  to  be  tested  by  adding  excess  of  am- 
monia or  sodium  acetate,  and  then  to  add  the  powdered  dimethyl- 

*  Von  Knorre  has  subsequently  suggested  that  the  oxalic  acid  may  be  omitted. 
Zeit.  Angw.  Chem.,  1893,  264. 

f  L.  Tschugaeff.  Ber.,  1905,  38,  2520-2522.  Jour.  Soc.  Chem.  Ind.,  XXIV, 
941. 


NICKEL  AND   COBALT.  197 

glyoxime,  and  to  boil  for  a  short  time.  Distinct  indications  are 
obtained  with  solutions  containing  only  one  part  of  nickel 
per  400,000  of  water.  The  reaction  is  not  disturbed  by  the 
presence  of  ten  times  as  much  cobalt  as  nickel,  but  when  the 
proportion  of  cobalt  is  much  greater  than  that  of  nickel,  it  is 
best  to  add  a  very  large  excess  of  ammonia  to  the  liquid  and  to 
shake  repeatedly,  excess  of  the  dimethyl  glyoxime  being  then 
added  and  the  solution  boiled  for  a  short  time.  In  testing  by 
this  method  for  nickel  in  such  products  as  commercial  cobalt 
salts,  the  reaction  is  .manifested  by  the  appearance  of  a  scarlet 
scum  rising  up  the  walls  of  the  test-tube,  but  it  is  generally 
necessary  to  filter  or  siphon  off  the  cooling  liquid  and  wash  the 
residue  with  water;  in  the  presence  of  nickel  this  residue  is  red, 
but  if  nickel  is  absent,  it  is  quite  colorless.  In  this  way  one  part 
of  nickel  can  be  detected  when  admixed  with  5000  parts  of 
cobalt. 

17.  Sensitive  Test  for  Cobalt.* — If  a  concentrated  solution 
of  ammonium  sulphocyanate  is  added  to  a  cobaltous  solution, 
the  latter  becomes  a  beautiful  blue,  owing  to  the  formation  of 
ammonium  cobaltous  sulphocyanate.  On  adding  water  the  blue 
color  disappears  and  the  pink  color  of  the  cobaltous  salt  takes 
its  place.  If,  now,  amyl  alcohol  is  added  (or  a  mixture  of  equal 
parts  of  amyl  alcohol  and  ether),  and  the  solution  is  shaken,  the 
upper  alcoholic  layer  is  colored  blue.  This  reaction  is  so  sen- 
sitive that  the  blue  color  is  recognizable  when  the  solution  con- 
tains only  0.02  mg.  of  cobalt.  Nickel  salts  produce  no  coloration 
of  the  amyl  alcohol.  If,  however,  iron  is  present,  the  red  Fe(CNS)a 
is  formed,  which  likewise  colors  the  amyl  alcohol,  making  the 
blue  color  (due  to  cobalt)  very  indistinct,  so  that,  under  some  con- 
ditions, it  can  no  longer  be  detected.  If,  however,  some  sodium 

*  Vogel's  reaction.     From  Tread  well's  Analytical  Chemistry   (Hall),  Vol.  I, 
P-  137. 


198  TECHNICAL   METHODS  OF  ORE   ANALYSIS. 

carbonate  solution  is  added,  the  iron  will  be  precipitated  as  ferric 
hydroxide,  while  the  blue  color  produced  by  the  cobalt  is  unaffected. 

18.  Separation  of  Nickel  from  Cobalt  as  Nickel  Glyoxime, 
Ni(C4H7N2O2)2.* — Determine  the  nickel  and  cobalt  together  by 
electrolysis,  as  previously  described.    Dissolve  the  deposit  in  nitric 
acid  and  replace  the  latter  by  evaporation  with  hydrochloric 
acid.     Dilute  the  neutral  or  slightly  acid  solution  so  that  not 
more  than  o.i  gram  of  cobalt  is  present  in  100  cc.,  heat  nearly 
to  boiling  and  add  somewhat  more  than  the  theoretical  amount 
of  an  alcoholic  solution  of  dimethyl  glyoxime.     Now  add  ammo- 
nia cautiously  until  the  solution  smells  slightly.     While  the  liquid 
is  still  hot,  filter  the  precipitate  through  a  Gooch  crucible,  wash 
with  hot  water  and  dry  at  uo°-i2o°  C.  for  45  minutes.     It 
contains  20.32  per  cent,  of  nickel.     The  precipitate  is  red  and 
crystalline.     It  contains  no  water  of  crystallization  and  sublimes 
at  250°  C.  without  decomposition. 

19.  Determination  of  Nickel  in  Steel,  f — Dissolve  about  0.5 
gram  of  the  steel  in  10  cc.  of  strong  hydrochloric  acid,  add  suffi- 
cient nitric  acid  to  completely  oxidize  the  iron,  and,  if  silica 
separates,  add  also  a  little  hydrofluoric  acid.     Finally,  add  2  or 
3  grams  of  tartaric  acid  and  dilute  the  solution  to  about  300  cc. 
Carefully  test  the  solution  to  see  if  enough  tartaric  acid  is  present 
to  prevent  any  precipitation  of  iron  when  the  solution  is  made 
alkaline  with  ammonia,  and  add  more  tartaric  acid  if  necessary. 
Now  neutralize  the  solution  so  as  to  leave  it  slightly  acid,  heat 
nearly  to  boiling  and  add  20  cc.  of  a  one  per  cent,  alcoholic  solu- 
tion of  dimethyl  glyoxime;  then  very  carefully  neutralize  the  slight 
excess  of  acid  with  ammonia,  leaving  the  solution  so  that  it  barely 
smells  of  this  reagent.     Filter  the  hot  mixture  through  a  Gooch 
filter,  wash  the  precipitate  with  hot  water  and  dry  at  no°-i2o° 

*  Treadwell's  Anal.  Chem.  (Hall),  ad  Ed.,  Vol.  II,  p.  125. 
f  Ibid.,  p.  146.     O.  Brunck,  Stahl  und  Eisen,  28,  331. 


NICKEL  AND    COBALT.  igg 

C.  for  45  minutes.     Weigh  as  Ni(C4H7N2O2)2,  containing  20.32 
per  cent,  of  nickel. 

The  determination  can  be  made  within  about  two  hours. 
The  results  are  accurate,  but  may  sometimes  appear  low  from 
the  fact  that  any  cobalt  present  is  not  determined  with  the  nickel, 
as  it  may  be  with  some  other  methods. 

20.  Volumetric  Method  for  Nickel. — In  the  following  method* 
nickel  may  be  accurately  determined  in  the  presence  of  aluminum, 
ferric  iron,  magnesium  and  zinc.  Manganese  and  copper  must 
be  removed.  Cobalt  counts  as  nickel.  If  present,  it  may  be 
detected  during  the  titration  by  the  darkening  of  the  solution. 
The  method  is  especially  applicable  to  the  assay  of  nickel  mattes 
and  German  silver.  In  the  case  of  ores  it  may  be  applied  to 
the  purified  solution  after  removing  iron,  manganese,  copper, 
etc.,  and  boiling  off  any  hydrogen  sulphide. 

The  following  solutions  are  required:  • 

Standard  silver  nitrate,  containing  about  3  grams  of  silver 
per  liter.  The  strength  of  this  solution  must  be  accurately  known. 

Potassium  iodide,  10  per  cent,  solution. 

Potassium  cyanide,  22  to  25  grams  per  liter.  This  solution 
must  be  tested  every  few  days.f 

Standardizing  the  Cyanide  Solution.  —  First,  accurately  estab- 
lish the  relation  of  the  cyanide  to  the  silver  solution.  Run  into 
a  beaker  3  or  4  cc.  of  the  former,  dilute  this  with  about  150 
cc.  of  water,  render  slightly  alkaline  with  ammonia,  and  then 
add  a  few  drops  of  the  potassium  iodide.  Now  carefully  run  in 
the  silver  solution  until  a  faint  permanent  opalescence  is  pro- 
duced, which  is  finally  caused  to  disappear  by  the  further  addi- 
tion of  a  mere  trace  of  cyanide.  The  respective  volumes  of  the 
silver  and  cyanide  solutions  are  then  read  off,  and  the  equivalent 

*  T.  Moore,  Chem.  News,  72,  92. 

t  The  addition  of  about  5  grams  of  potassium  hydroxide  per  liter  is  said  to 
increase  its  permanency. 


200  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

in  cyanide  of  i  cc.  of  silver  solution  calculated.  Now  calculate 
the  metallic  silver  value  of  i  cc.  of  the  cyanide  solution  and 
multiply  this  by  0.27193  to  obtain  the  nickel  value. 

Titration  of  a  Nickel  Solution.  —  The  nickel  solution  (con- 
taining not  more  than  about  o.i  gram  of  nickel)  must  have 
sufficient  free  acid  present  to  prevent  the  formation  of  any 
precipitate  on  the  subsequent  addition  of  ammonia  to  alkaline 
reaction;  if  this  is  not  the  case,  a  little  ammonium  chloride  may 
be  added.  Make  distinctly  alkaline  with  ammonia,  add  a  few 
drops  of  the  potassium  iodide  solution  and  dilute  to  150  or  200 
cc.  A  few  drops  of  the  silver  solution  are  now  run  in  and  the 
solution  stirred  to  produce  a  uniform  turbidity.  Cool  the 
mixture  to  at  least  20°  C.  and  it  is  ready  to  be  titrated  with  the 
potassium  cyanide  solution,  which  is  added  slowly  and  with 
constant  stirring  until  the  precipitate  wholly  disappears;  a  few 
extra  drops  are  added,  after  which  the  beaker  is  placed  under 
the  silver  nitrate  burette,  and  this  solution  gently  dropped  in 
until  a  faint  permanent  turbidity  is  again  visible;  this  is  now 
finally  caused  to  dissolve  by  the  mere  fraction  of  a  drop  of  the 
cyanide.  A  correction  must  now  be  applied  for  the  excess  of 
cyanide  added,  by  noting  the  amount  of  silver  solution  employed 
and  deducting  its  value  in  cyanide  solution  from  the  amount  of 
the  latter  used.  The  amount  of  cyanide  solution  actually 
consumed  by  the  nickel  is  thus  arrived  at,  from  which  the  per- 
centage of  nickel  is  calculated. 

In  the  presence  of  aluminum,  magnesium  or  ferric  iron,  they 
may  be  kept  in  solution  with  either  citric  acid,  tartaric  acid  or 
isodium  pyrophosphate.  In  the  presence  of  zinc,  use  sodium 
pyrophosphate.  The  action  of  iron  is  somewhat  deceptive, 
as  the  solution,  once  cleared  up,  often  becomes  troubled  again 
on  standing  for  a  minute;  should  this  occur,  a  further  addition 
of  cyanide  must  be  given  until  the  liquid  is  rendered  perfectly 


NICKEL  AND    COBALT.  201 

limpid.  The  temperature  of  the  solution  should  never  exceed 
20°  C.:  above  this  the  results  become  irregular.  The  amount 
of  free  ammonia  also  has  a  disturbing  influence;  a  large  excess 
hinders  or  entirely  prevents  the  reaction;  the  liquid  should,  there- 
fore, be  only  slightly  but  very  distinctly  alkaline.  The  potassium 
cyanide  should  be  as  pure  as  possible.  The  most  hurtful  im- 
purity is  sulphur,  which  causes  a  darkening  of  the  solution 
owing  to  the  formaion  of  the  less  readily  soluble  silver  sulphide. 
To  get  rid  of  the  sulphur  impurity  it  is  necessary  to  thoroughly 
agitate  the  cyanide  liquor  with  lead  oxide,  or,  what  is  far  pref- 
erable, bismuth  oxide. 

In  the  hands  of  Mr.  Moore,  the  above  method,  after  many 
thousands  of  determinations,  has  been  found  to  be  more  accurate 
and  reliable  than  either  the  electrolytic  or  gravimetric  methods. 

21.  Modification  of  the  Above  Method,  Applied  to  the  Deter- 
mination of  Nickel  in  Nickel  Steel.* — The  determination  can  be 
made  with  speed  and  accuracy,  even  in  the  presence  of  iron, 
manganese,  chromium,  zinc,  vanadium,  molybdenum  and  tungsten. 

Requirements.  The  potassium  cyanide  solution  should  be 
about  equivalent  to  a  tenth-normal  silver  solution,  and  is  pre- 
pared by  dissolving  13.5  grams  of  pure  potassium  cyanide  and 
5  grams  of  potassium  hydroxide  in  water  and  diluting  to  i  liter. 

The  silver  nitrate  solution  is  made  exactly  tenth-normal  and 
is  prepared  by  dissolving  8.495  grams  of  AgNO3  in  water  and 
diluting  to  exactly  500  cc.  i  cc.  of  this  solution  is  equivalent  to 
0.01302  grams  KCN,  or  to  0.002934  grams  Ni.  It  is  used  for 
standardizing  the  potassium  cyanide  solution,  and  in  the  analysis 
itself. 

The  potassium  iodide  solution  contains  2  grams  KI  in  100  cc. 

Determination.     Dissolve  i  gram  of  the  steel  in  a  casserole 

*  Treadwell's  Anal.  Chem.  (Hall),  ad  Ed.,  p.  656.  Numerous  references  are 
given. 


202  TECHNICAL   METHODS  OF  ORE   ANALYSIS. 

with  TO  to  15  cc.  of  nitric  acid  (sp.  gr.  1.20),  adding  a  little 
hydrochloric  acid  if  necessary.  After  the  steel  has  dissolved, 
add  6  to  8  cc.  of  sulphuric  acid  (1:1)  and  evaporate  until  fumes 
of  the  latter  begin  to  come  off.  Cool  the  residue,  add  30  to  40 
cc.  of  water  and  heat  until  the  anhydrous  ferric  sulphate  has 
all  dissolved.  Transfer  the  solution  to  a  400-0:.  beaker,  filtering 
if  necessary,  and  add  13  grams  of  sodium  pyrophosphate  dis- 
solved in  60  cc.  of  water  at  about  60°  C.  The  pyrophosphate 
solution  must  not  be  boiled,  as  this  causes  the  formation  of  nor- 
mal phosphate.  The  addition  of  the  sodium  pyrophosphate  pro- 
duces a  heavy  white  precipitate  of  ferric  pyrophosphate.  Cool 
the  liquid  to  room  temperature  and  add  dilute  ammonia  (1:1), 
drop  by  drop,  while  stirring  constantly,  until  the  greater  part  of 
the  precipitate  has  dissolved  and  the  solution  has  assumed  a 
greenish  tinge.  At  this  point  it  should  react  alkaline  toward 
litmus,  but  should  not  smell  of  free  ammonia.  Now  heat  the 
solution  gently,  while  stirring,  and  the  remainder  of  the  pyro- 
phosphate will  dissolve,  giving  a  perfectly  clear  light  green  solu- 
tion. If  the  ammonia  is  added  too  fast,  or  the  solution  is  not 
carefully  stirred,  a  brownish  color  is  likely  to  result, -but  this  can 
usually  be  overcome  by  carefully  adding  a  few  drops  of  dilute 
sulphuric  acid.  Cool  the  clear  solution  to  room  temperature  and 
add  5  cc.  of  the,  standard  silver  nitrate  solution  together  with  5 
cc.  of  the  potassium  iodide.  Now  titrate  the  solution  with  the 
potassium  cyanide,  adding  it  until  the  precipitate  of  silver  iodide 
has  disappeared.  Finish  the  titration  by  adding  just  enough  more 
of  the  silver  nitrate  to  again  produce  a  slight  turbidity.  Before 
calculating  the  percentage  of  nickel,  make  a  correction  for  the 
amount  of  silver  nitrate  added. 

Remarks. — The  results  obtained  by  the  potassium  cyanide 
titration  of  nickel  are  said  to  be  very  satisfactory.  It  can  be 
carried  out  in  the  presence  of  most  of  the  other  elements  of  the 


NICKEL    AND   COBALT,  203 

ammonium  sulphide  group.*  If  copper  is  present  in  amounts 
not  exceeding  0.4  per  cent.,  the  copper  will  replace  almost  exactly 
three-quarters  of  its  weight  of  nickel.  In  case  chromium  is 
present,  the  dark  color  due  to  the  presence  of  chromic  salts  may 
be  obviated  by  adding  to  the  original  sulphuric  acid  solution  a 
two  per  cent,  solution  of  potassium  permanganate  until  a  slight 
permanent  precipitate  of  manganese  dioxide  is  obtained,  whereby 
the  chromium  is  oxidized  to  chromic  acid.  The  solution  is 
filtered,  concentrated  in  a  400  cc.  beaker  to  about  60  cc.,  then 
treated  with  sodium  pyrophosphate,  as  described  above.  The 
method  is  not  applicable  in  the  presence  of  cobalt,  but  when  the 
amount  of  the  latter  does  not  exceed  one-tenth  the  amount  of 
nickel  present,  the  titration  can  be  carried  out  successfully  and 
the  results  represent  the  amount  of  nickel  and  cobalt  present. 

22.  Electrolytic  Method  in  General  Use  at  Cobalt,  Ont., 
Canada. f — Treat  i  gram  of  the  ore  in  a  25o-cc.  beaker  with  10 
cc.  of  strong  nitric  acid  and  5  cc.  of  strong  hydrochloric  acid. 
When  decomposition  is  complete  add  15  cc.  of  strong  sulphuric 
acid  and  boil  until  the  sulphuric  acid  is  fuming  strongly.  Allow 
to  cool,  take  up  with  water,  add  5  cc.  of  strong  hydrochloric  acid 
to  assist  solution  and  boil  gently  for  a  few  minutes.  Remove  from 
the  heat  and  pass  hydrogen  sulphide  through  the  hot  solution  for 
ten  to  fifteen  minutes,  then  heat  again  and  once  more  pass  in 
hydrogen  sulphide  until  all  the  arsenic  is  precipitated  and  the  super- 
natant liquid  is  clear.  Filter,  washing  the  precipitate  six  or  seven 
times  with  hot  water.  Boil  the  filtrate  to  expel  the  hydrogen 
sulphide  and  reduce  to  a  volume  of  about  150  cc.  Filter  and 
wash  as  before.  Heat  the  filtrate  to  boiling  and  add  15  to  20 


*  Instead  of  using  sodium  pyrophosphate  to  prevent  the  interference  of  iron 
and  other  metals,  many  chemists  use  citric  or  tartaric  acid. 

f  Communicated  by  Mr.  B.  C.  Lamble,  chemist  at  the  La  Rose  Mines,  Ltd., 
Cobalt. 


204  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

cc.  of  hydrogen  peroxide  to  effect  oxidation.  After  boiling  a  short 
time,  remove  from  the  heat  and  allow  to  cool  somewhat  and  then 
separate  the  iron  as  basic  acetate  as  follows:  Make  the  solution 
just  alkaline  with  ammonia  and  then  reacidify  slightly  with  hydro- 
chloric acid.  Add  15  grams  of  solid  sodium  acetate  (crystals)  and 
boil.  Filter  off  the  iron  precipitate,  washing  with  hot  water,  and 
place  the  nitrate  over  the  heat  to  concentrate.  Dissolve  the  pre- 
cipitate in  hot  dilute  hydrochloric  acid,  dilute  to  about  150  cc.  and 
repeat  the  precipitation  as  just  described.  Unite  the  two  nitrates, 
boil  down  to  about  100  cc.  and  filter.  Make  the  filtrate  alkaline 
with  ammonia  and  add  about  20  cc.  in  excess.  Electrolyze  the 
hot  solution  (which  should  have  a  volume  of  125  to  130  cc.), 
keeping  it  hot  during  the  electrolysis  and  highly  ammoniacal. 
(See  12.)  When  the  operation  is  apparently  finished  (in  from 
2\  to  3^-  hours),  test  for  nickel  and  cobalt  on  a  spot-plate  with 
ammonium  sulphide.  Wash  the  cathode  first  with  water,  then 
with  alcohol,  dry  at  about  100°  C.,  and  weigh.  This  gives  the 
combined  nickel  and  cobalt. 

Dissolve  the  deposit  in  a  25o-cc.  beaker  in  strong  nitric  acid 
and  wash  off  the  cathode  with  hot  water.  Boil  or  evaporate  the 
solution  to  a  syrup.  Add  about  20  cc.  of  water  and  then  add 
a  solution  of  potassium  hydroxide  until  a  precipitate  of  cobalt 
hydroxide  (blue)  remains  undissolved.  Now  acidify  with  acetic 
acid  and  add  a  few  cubic  centimeters  in  excess;  then  add  about 
25  grams  of  potassium  nitrite  and  stir  until  dissolved.  Boil 
gently  for  about  twenty  minutes,  then  dilute  with  water  until  the 
beaker  is  about  five-sixths  full  and  allow  to  stand  over  night. 
Decant  and  filter  the  cobalt  precipitate  and  wash  it  a  few  times 
with  ice-cold  water,  or  water  containing  about  five  per  cent,  of 
potassium  nitrite  and  barely  acidified  with  acetic  acid.  Dissolve 
the  precipitate  in  hot  dilute  sulphuric  acid  and  boil  down  the 
solution  until  the  sulphuric  acid  is  fuming.  Cool,  dilute  with 


NICKEL  AND  COBALT. 


205 


water,  heat  to  boiling  and  filter.  Make  the  filtrate  alkaline  with 
ammonia,  having  about  20  cc.  in  excess,  dilute  to  about  125  cc. 
and  electrolyze  as  described  above.  This  gives  the  cobalt,  and 
the  nickel  is  determined  by  the  difference  between  this  weight 
and  that  of  the  combined  nickel  and  cobalt. 

NOTE. — I  would  recommend  an  8-oz.  flask  instead  of  a  beaker 
for  the  decomposition,  and  7  cc.  of  sulphuric  acid  instead  of  15 
cc.  Any  globules  of  separated  sulphur  may  be  completely  vola- 
tilized by  allowing  the  sulphuric  acid  to  boil  very  gently  for  some 
time  after  coming  to  fumes.  In  electrolyzing,  Mr.  Lamble  dilutes 
the  solution  to  about  300  cc.  and  employs  a  gauze  cathode. 


CHAPTER    XXII. 

PHOSPHORUS. 

i.  Gravimetric  Method  for  Iron  Ores.*— Take  1.63  grams 
of  the  finely  ground  ore.  Dissolve  by  boiling  gently  for  20  minutes 
with  40  cc.  of  strong  hydrochloric  acid  (1.20  sp.  gr.)  in  a  covered 
8-oz.  beaker.  Dilute  with  20  cc.  of  water  and  filter,  washing 
with  water.  Receive  the  filtrate  in  an  8-oz.  beaker.  Evaporate 
the  filtrate  to  dryness  on  a  sand-bath  or  hot  plate.  While  the 
filtrate  is  evaporating  ignite  the  filter  and  insoluble  residue  in  a 
platinum  crucible.  After  the  paper  is  burned  off,  break  up  any 
lumps  with  a  platinum  rod  and  then  ignite  again  at  a  red  heat 
for  about  2  minutes.  Cool,  and  transfer  the  ignited  residue  to 
the  beaker  in  which  the  filtrate  is  evaporating.  Any  phosphorus 
that  remained  with  the  insoluble  residue  is  thus  rendered  soluble 
by  the  ignition  and  recovered,  f  After  evaporation,  add  to  the 
residue  in  the  beaker  25  cc.  of  strong  nitric  acid  (sp.  gr.  1.42), 
cover  the  beaker  and  boil  to  about  12  cc.  Now  dilute  with 
12  cc.  of  water  and  filter,  washing  with  water.  Receive  the 
filtrate  in  an  8-oz.  flask.  The  total  bulk  should  not  exceed  50  cc. 
Heat  to  4O°-45°  C.,  add  60  cc.  of  molybdate  solution,!  previously 

*  Mainly  the  method  of  John  S.  Unger,  Trans.   Engineers  Soc.  of  Western 
Penn.,  1896. 

f  Mixer  and  Dubois.     Jour.  Am.  Chem.  Soc.,  XIX,  p.  614. 
j  See  below,  7. 

206 


PHOSPHORUS.  207 

filtered  and  heated  to  4o°-45°  C.,  stopper  the  flask  and  shake 
for  5  minutes.  Allow  to  stand  in  a  warm  place  for  15  minutes 
and  then  filter  through  a  7 -cm.  washed  filter  (Baker  and  Adamson, 
A  grade)  that  has  been  previously  dried  at  110°  C.  and  weighed. 
Wash  with  a  2  per  cent,  nitric  acid  solution  till  free  from  iron, 
and  then  twice  with  95  per  cent,  alcohol.  Dry  20  minutes  at 
no°C.  and  weigh.  The  dried  residue  contains  1.63  percent 
of  phosphorus,  therefore  each  milligram  found  corresponds  to 
o.ooi  per  cent,  of  phosphorus  in  the  ore. 

2.  Error  Caused  when    Titanium  is  Present. — Blair  *  notes 
the  fact  that  if  a  solution  of  ferric  chloride  containing  titanic  and 
phosphoric  acids  is  evaporated  to  dryness,  a  compound  of  TiO2, 
P2Os,   and  Fe2Os  is  formed  which  is  completely  insoluble  in 
hydrochloric  acid  (and  presumably  in  nitric  acid  also).     When 
titanium  is  present  in  the  material  analyzed  and  such  a  residue 
is  obtained,  on  filtering  the  nitric  acid  solution  after  evaporation 
to  dryness,  it  may  be  treated  as  follows: 

3.  Dry  the  residue  and  burn  off   the  filter  paper  by  ignition 
in  a  platinum  crucible.     Moisten  the  cool  residue  with  a  few 
drops  of  strong  sulphuric  acid  and  add  sufficient  hydrofluoric 
acid  to  dissolve  the  silica.     Evaporate  cautiously  and  heat  until 
all  the  sulphuric  acid  is  driven  off.     Cool,  add  2  or  3  grams  of 
sodium  carbonate  and  fuse  the  mixture.     Dissolve  the  melt  in 
hot  water,   filter  and  wash.     Receive  the  filtrate  in  a  6-oz.  flask 
and  acidify  with  nitric  acid.     The  total  bulk  should  not  exceed 
50  cc.     Heat  to  4o°-45°  C.,  add  25  cc.  of  molybdate  solution, 
previously   filtered   and   heated   to   the   same   temperature,   and 
finish   as   described   above   for  the   main   solution.     The   same 
filter,  if  desired,  may  be  used  for  both  nitrations  of  the  yellow 
precipitate. 

4.  The  presence  of  titanium  in  an  ore,  if  much  is  present, 

*  Chem.  Anal,  of  Iron,  3d  Ed.,  p.  86. 


208  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

may  be  recognized  by  the  peculiar  milky  appearance  of  the 
solution  when  it  is  diluted  before  filtering  off  the  insoluble  matter, 
and  by  the  tendency  of  the  latter  to  run  through  the  filter  when 
washed  with  water.  In  cases  of  uncertainty  it  is  best  to  assume 
that  titanium  is  present  and  proceed  with  the  residue  as  described 
above.  If  the  residue  left  after  filtering  the  aqueous  solution 
of  the  melt  of  3  be  dissolved  in  dilute  hydrochloric  acid,  the 
solution  placed  in  a  test-tube  and  metallic  zinc  added,  the  liquid 
will  become  first  colorless,  from  the  reduction  of  the  ferric  iron, 
then,  if  titanium  be  present,  pink  or  purple  and  finally  blue,  from 
the  formation  of  Ti2Os. 

5.  Method  for  Steel. — Dissolve  1.63  grams  of  the  steel,  in  a 
6-oz.  Erlenmeyer  flask,  in  30  cc.  of  nitric  acid  of  about  1.20  sp.  gr. 
Evaporate  by  boiling  over  a  naked  flame  to  15  cc.,  add  to  the 
boiling  solution  20  cc.  of  chromic  acid  solution   (see  8  below) 
and  again  evaporate  to  18  cc.     Remove  from  the  heat  and  wash 
down  the  sides  of  the  flask  with  from  5-7  cc.  of  water  and  cool 
to  4o°-45°  C.     Proceed  from  this  point  as  directed  above  for 
ores   (i).     As    in    the    case    of  ores,  each   milligram  of  yellow 
precipitate  found  corresponds  to  o.ooi  per  cent,  of  phosphorus 
in  the  steel. 

6.  Method  for  Pig  Iron. — Dissolve  1.63  grams,  in  a  4j-inch 
covered  evaporating-dish,  in  40  cc.  of  strong  nitric  acid  (sp.  gr. 
1.42).     When  action  has  ceased,  remove  the  cover  and  evaporate 
to   dryness   on   a   sand-bath.     Place   the  dish   and   dry   residue 
over  a  burner  and  heat  cautiously  with  the  naked  flame  until 
the  mass  ceases  to  evolve  red  fumes.     Allow  to  cool,  add  25  cc. 
of  strong  hydrochloric  acid  (sp.  gr.  1.20),  cover  with  a  watch- 
glass  and  boil  to  10  cc.     Add  cautiously  25  cc.  of  strong  nitric 
acid  (sp.  gr.  1.42)  and  boil  to  12  cc.     Remove  from  the  heat, 
rinse  off  the  watch-glass  and  wash  down  the  sides  of  the  dish, 
using  about  12  cc.  of  water,  and  then  filter  through  an  n-cm. 


PHOSPHORUS.  209 

filter  into  an  8-oz.  flask,  washing  with  water.  The  solution  should 
not  exceed  50  cc.  in  bulk.  Heat  to  4o°-45°  C.  and  finish  as 
described  above  for  ores  (i).  Each  milligram  of  yellow  precip- 
itate found  corresponds  to  o.ooi  per  cent,  of  phosphorus  in  the 
pig  iron. 

7.  Molybdic  Acid  Solution.* — Mix  100  grams  of  molybdic  acid 
acid  to  a  paste  with  265  cc.  of  water.    Add  155  cc.  of  strong 
ammonia  water  (sp.  gr.  0.90)  and  stir  until  all  is  dissolved.     To 
this  solution  add  66  cc.  of  strong  nitric  acid  (sp.  gr.  1.42),  stir 
well  and  then  set  aside  for  an  hour.     In  another  vessel  make  a 
mixture  of  395  cc.  of  strong  nitric  acid  and  noo  cc.  of  water. 
Finally,  pour  the  first  solution  into  the  second,  stirring  constantly. 
Allow  to  stand  for  24  hours  before  using. 

8.  Chromic    Acid    Solution.  —  Dissolve   30    grams   of    pure 
chromic  acid  in  2  liters  of  strong  nitric  acid  (sp.  gr.  1.42),  warm- 
ing gently.     This  solution  must  be  made  up  fresh  at  least  every 
two  weeks. 

9.  Volumetric  Method  for  Iron  Ores,  Steel,  etc. — Start  with 
2  grams  of  material  and,  according  to  its  nature,  proceed  by 
one  of  the  above-described  methods  until  the  yellow  precipitate 
is  finally  obtained  on  the  filter,  which  need  not  be  weighed. 
Wash  with  a  solution  of  acid  ammonium  sulphate,  prepared  by 
adding  15  cc.  of  strong  ammonia  (sp.  gr.  0.90)  and  25  cc.  of 
strong  sulphuric  acid  (sp.  gr.   1.84)  to  i  liter  of  water.     Wash 
until  2  or  3  cc.  of  the  wash-water  give  no  brown  reaction  for 
molybdenum  when  tested  with  a  drop  of  ammonium  sulphide. 
Place  the  flask  in  which  the  precipitation  was  made  under  the 
funnel  and  dissolve  the  ammonium  phosphomolybdate  on  the 
filter  by  pouring  over  it  a  warm  mixture  of  5  cc.  of  strong  ammonia 
water  and  20  cc.  of  water.     Wash  the  filter  with  water  until 

*  See  1 2. 


210  TECHNICAL  METHODS  OF  ORE   ANALYSIS. 

the  filtrate  measures  75  cc.  Now  add  5  grams  of  pulverized 
pure  zinc,  ioo-mesh,  pouring  it  through  a  funnel  to  prevent  any 
zinc  from  clinging  to  the  sides  of  the  flask.  Then  add,  cau- 
tiously, 15  cc.  of  strong  sulphuric  acid,  best  by  letting  it  run 
from  a  glass-stoppered  burette.  It  is  a  good  plan,  although  not 
absolutely  necessary,  to  close  the  flask  with  a  rubber  stopper 
carrying  a  glass  tube  bent  twice  at  right  angles,  the  outer  arm 
dipping  into  a  beaker  containing  a  saturated  solution  of  sodium 
acid  carbonate.  Allow  the  flask  and  contents  to  stand  for  about 
30  minutes,  when,  if  all  action  has  ceased  and  there  is  no  appre- 
ciable residue  from  the  zinc,  the  solution  is  ready  to  titrate  with 
permanganate.  In  case  of  a  residue  (lead,  etc.),  that  might 
have  a  reducing  action  on  the  permanganate,  filter  the  solution 
through  a  rapid-running  filter  *  and  wash  with  luke-warm  water 
receiving  the  filtrate  in  a  flask.  The  solution  should  be  of  a  green 
<;olor.  If  brown,  the  result  will  come  low.  Bring  the  liquid  to  a 
temperature  of  about  40°  C.  and  titrate  with  standard  potassium 
permanganate  solution.  The  titrated  solution  gradually  becomes 
colorless  and  then,  at  the  end,  the  usual  pink  tinge  is  obtained. 

10.  A   blank    test   should   be   made   by   adding   to   another 
flask  70  cc.  of  water,  5  cc.  of  strong  ammonia,  5  grams  of  the 
ioo-mesh  zinc  and  finally  15  cc.  of  strong  sulphuric  acid,  and 
treating  this  flask  precisely  like  the  other.     The  amount  of  per- 
manganate used  by  this  test  should  be  deducted  from  the  amount 
used  in  the  analysis  of  the  substance. 

The  iron  value  of  the  permanganate  solution  multiplied  by 
0.01541  will  give  the  phosphorus  value. 
This  may  be  determined  as  follows: 

11.  When   molybdic   acid   is   reduced   to   Mo2O3   the   latter 
requires  the  same  amount  of  oxygen  for  reoxidation  as  is  required 
to  oxidize  6FeO  to  the  ferric  state.     Therefore,  3Fe   (ferrous) 
are  equivalent  to  MoO3,  or,   167.7  parts  by  weight  of  Fe  are 

*  A  filter  of  absorbent  cotton  and  the  procedure  described  in  vm,  12,  is  best. 


PHOSPHORUS.  211 

equivalent  to  144  parts  of  MoOa.  Accordingly,  the  iron  factor 
of  the  permanganate  multiplied  by  0.8586  will  give  the  MoOa 
factor.  Now  the  formula  of  the  ammonium  phosphomolybdate 
is  (NH4)3i2MoO3.PO4,  therefore  1728  parts  by  weight  of  MoOs 
correspond  to  31  parts  of  P,  or,  i  part  of  MoO3  =  0.01795  parts  of 
P.  Thus  by  multiplying  the  iron  factor  of  the  permanganate  by 
0.8586,  and  the  product  by  0.01795, tne  phosphorus  factor  is  ob- 
tained, or,  the  Fe  factor,  multiplied  by  0.01541  gives  the  P  factor. 

12.  Note  Regarding  Molybdic  Acid. — The  substance  sold  as 
molybdic  acid  frequently  consists  to  a  greater  or  less  extent  of 
alkali  molybdate.     Such  material  may  be  used  for  phosphorus 
determinations    with   fairly  good    results    if    the    percentage    of 
molybdic  acid  is  determined  and  the  amount  of  substance  taken 
in  making  up  the  molybdate  solution  regulated  accordingly,  so 
that  the  full  quantity  of  molybdic  acid  shall  be  present.     The 
determination  may  be  made  by  weighing  o.i  gram,  dissolving  in 
a  mixture  of  70  cc.  of  water  and  5  cc.  of  strong  ammonia,  adding 
5  grams  of  loo-mesh  zinc  and  15  cc.  of  strong  sulphuric  acid, 
and  finally  titrating  the  reduced  solution  precisely  as  in  a  phos- 
phorous determination  (9). 

The  iron  factor  of  the  permanganate  multiplied  by  0.8586 
will  give  the  MoO3  factor  (10). 

A  yellow  molybdate  solution  indicates  the  presence  of  silica, 
and  a  phosphorus  determination  made  with  such  a  solution 
is  likely  to  come  high  owing  to  ammonium  silicomolybdate  being 
dragged  down  with  the  phosphomolybdate.  If  about  30  milli- 
grams of  microcosmic  salt  dissolved  in  a  little  water  be  added 
per  liter  of  yellow  molybdate  solution,  the  mixture  agitated  and 
then  allowed  to  settle  24  hours,  the  solution  will  become  colorless 
and  fit  for  use. 

13.  Method    for   Limestone.  —  Treat    20    grams    in  a  large 
covered  beaker  with  sufficient  strong  hydrochloric  acid  to  effect 


212  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

solution.  Add  the  acid  cautiously,  a  little  at  a  time,  with  agita- 
tion, to  avoid  frothing  over  the  beaker.  When  enough  acid  has 
been  added  and  effervescence  has  ceased,  warm  gently  if  necessary 
to  dissolve  any  separated  iron  compounds.  Solution  being 
finally  as  complete  as  possible,  dilute  sufficiently  with  cold  water 
and  filter,  washing  filter  and  residue  with  cold  water.  To  the 
filtrate  add  a  few  drops  of  ferric  chloride  solution  (not  necessary, 
of  course,  if  the  solution  already  contains  sufficient  iron)  and 
then  ammonia  until  the  solution  is  alkaline  to  litmus  paper. 
If  the  precipitate,  containing  the  phosphorus  as  ferric  phosphate, 
is  not  decidedly  reddish-brown  in  color,*  acidulate  again  with 
hydrochloric  acid,  add  more  ferric  chloride  solution  and  then 
ammonia  once  more  to  alkaline  reaction.  Now  add  acetic  acid 
to  decided  acid  reaction.  Boil  for  a  few  minutes,^  filter,  wash 
once  with  hot  water  and  then  dissolve  in  warm  dilute  hydro- 
chloric acid  on  the  filter,  receiving  the  solution  in  the  beaker  in 
which  the  precipitation  was  made.  Reserve  this  solution  for  the 
present. 

14.  The  original  insoluble  residue  may  contain  phosphorus. 
Ignite  it  in  platinum  until  the  carbon  of  the  filter  is  all  burned 
off,  break  up  any  lumps  with  a  platinum  rod  and  then  ignite  at 
a  red  heat  for  2  or  3  minutes.  Cool,  moisten  with  water,  add  a 
little  hydrochloric  acid  and  warm  to  dissolve  the  soluble  matter. 
Dilute  and  filter  through  the  last  filter  used  above,  receiving  the 
filtrate  in  the  beaker  containing  the  reserved  solution  Dilute  this 
solution  and  reprecipitate  exactly  as  before  with  ammonia  and 
acetic  acid.  Dissolve  this  precipitate  on  the  filter  in  warm  dilute 
hydrochloric  acid,  receiving  the  solution  in  a  small  beaker  and 
washing  the  filter  with  hot  water.  Evaporate  the  solution  in 
the  beaker  almost  to  dryness  to  expel  the  excess  of  hydrochloric 

*  Ferric  phosphate  is  white  and  the  red  color  indicates  the  necessary  excess  of 
iron  precipitated  as  ferric  hydroxide. 


PHOSPHORUS.  213 

acid,  and  then  add  to  it  a  filtered  solution  of  5  or  10  grams  of 
citric  acid  (according  to  the  size  of  the  ferric  precipitate)  dissolved 
in  10-20  cc.  of  water.  Next,  adcl  5  to  10  cc.  of  magnesia  mixture  * 
and  enough  ammonia  to  make  the  liquid  faintly  alkaline.  Stand 
the  beaker  in  cold  water  until  perfectly  cold  and  then  add  to 
the  solution  one-half  its  volume  of  strong  ammonia  and  stir  well. 
When  the  precipitate  of  NH4MgPO4  has  begun  to  form,  stop 
stirring  and  allow  the  beaker  to  stand  in  cold  water  for  10  or  15 
minutes,  then  stir  vigorously  several  times  at  intervals  of  a  few 
minute's,  and  finally  allow  the  mixture  to  stand  over  night.  Filter 
on  a  small  ashless  filter  and  wash  with  a  mixture  of  i  part  strong 
ammonia  and  2  parts  water  and  containing  also  2.5  grams  of 
ammonium  nitrate  in  100  cc. 

15.  Dry  the  filter  and  precipitate  and  ignite  them  in  a  weighed 
platinum  crucible,  first  at  a  very  low  temperature  so  as  to  carbon- 
ize the  filter  without  decomposing  the  precipitate.  Now  break 
up  the  residue  with  a  platinum  rod  and  then  heat  at  a  gradually 
increasing  temperature  to  the  full  power  of  a  Bunsen  burner  and 
continue  the  ignition  until  the  residue  is  perfectly  white. '  Cool 
and  weigh.  Now  fill  the  crucible  half  full  of  hot  water,  add 
from  5  to  20  drops  of  strong  hydrochloric  acid  and  heat  until 
the  precipitate  has  dissolved.  Filter  off  on  another  small  ashless 
filter  any  silica  or  ferric  oxide  that  may  remain,  ignite  and  weigh. 
The  difference  between  the  two  weights  is  the  weight  of  the 
Mg2P2O7,  which,  multiplied  by  0.27837,  will  give  the  weight  of 
the  phosphorus. 

*  Magnesia  mixture. — Dissolve  no  grams  of  crystallized  magnesium  chloride 
(MgCl2+  6H2O)  in  water  and  filter.  Dissolve  280  grams  of  ammonium  chloride  in 
water,  add  a  little  bromine  water,  and  a  slight  excess  of  ammonia,  and  filter. 
Add  this  solution  to  the  solution  of  magnesium  chloride,  add  enough  ammonia 
to  impart  a  decided  odor,  dilute  to  about  2  liters,  shake  vigorously  from  time  to 
time,  allow  to  stand  for  several  days,  and  filter  into  a  small  bottle  as  required  for 
use.  Ten  cc.  of  this  solution  will  precipitate  about  0.15  gram  of  P,O5.  Blair, 
Chem.  Anal,  of  Iron. 


CHAPTER    XXIIL 

POTASSIUM  AND  SODIUM. 

ALMOST  the  only  occasions  when  the  technical  metallurgical 
chemist  has  to  make  quantitative  determinations  of  potassium 
and  sodium  are  in  the  analyses  of  silicates,  such  as  clays,  etc. 
Descriptions  of  methods  will,  therefore,  be  confined  to  such  as 
apply  to  these  substances. 

i.  Method  of  J.  Lawrence  Smith.*  —  Principle.^- The  sub- 
stance is  heated  with  a  mixture  of  i  part  ammonium  chloride 
and  8  parts  calcium  carbonate.  By  this  means  the  alkalies  are 
obtained  in  the  form  of  chlorides,  while  the  remaining  metals 
are  for  the  most  part  left  behind  as  oxides,  and  the  silica  is  changed 
to  calcium  silicate,  as  represented  by  the  following  equation: 

2KAlSi3O8  +  6CaCO3  +  2NH4C1 

=  6CaSiO3  +  6CO2  + A12O3  -f  2KC1  +  2NH3  +  H2O. 

The  alkali  chlorides  together  with  the  calcium  chloride  can 
be  removed  from  the  sintered  mass  by  leaching  with  water,  while 
the  other  constituents  remain  undissolved. 

Preparation. — The  ammonium  chloride  necessary  for  the 
determination  is  prepared  by  subliming  the  commercial  salt; 
the  calcium  carbonate  by  dissolving  the  purest  calcite  obtainable 

*  This  description  of  Smith's  method  is  taken    from  Treadwell's  Analytical 
Chemistry,  Hall,  Vol.  II. 

214 


POTASSIUM  AND  SODIUM.  215 

in  hydrochloric  acid  and  precipitating  with  ammonia  and  am- 
monium carbonate.  This  last  operation  is  performed  in  a  large 
porcelain  dish.  After  the  precipitate  has  settled,  the  clear  solution 
is  poured  off  and  the  precipitate  is  washed  by  decantation  until 
free  from  chlorides.  The  product  thus  obtained  contains  traces 
of  alkalies,  but  the  amount  present  is  determined  once  for  all  by 
a  blank  test  and  a  corresponding  deduction  made  from  the  results 
of  the  analysis;  it  is  usually  sodium  chloride  and  amounts  to 
0.0012-0.0016  gram  for  8  grams  calcium  carbonate.  The  decom- 
position was  performed  by  Smith  in  a  finger-shaped  crucible 
about  8  cm.  long  and  with  a  diameter  of  about  2  cm.  at  the  top 
and  ij  cm.  at  the  bottom.  Such  a  crucible  is  suitable  for  the 
decomposition  of  about  0.5  gram  of  the  mineral.  A  larger 
quantity  can  be  analyzed  in  an  ordinary  platinum  crucible. 

Filling  the  Crucible. — About  0.5  gram  of  the  mineral  is  mixed 
with  an  equal  quantity  of  sublimed  ammonium  chloride  by 
trituration  in  an  agate  mortar,  then  3  grams  of  calcium  carbonate 
are  added  and  intimately  mixed  with  the  former.  The  mixture 
is  transferred  to  a  platinum  crucible  with  the  help  of  a  piece  of 
glazed  paper,  and  the  mortar  is  rinsed  with  i  gram  of  calcium 
carbonate,  which  is  added  to  the  contents  of  the  crucible. 

The  Ignition. — The  covered  crucible  is  placed  in  a  slightly 
inclined  position  and  gradually  heated  over  a  small  flame  until 
no  more  ammonia  is  evolved  *  (this  should  take  about  15  min- 
utes), then  the  temperature  is  raised  until  finally  the  lower  three- 
fourths  (and  no  more)  of  the  crucible  are  brought  to  a  dull  red 
heat,  and  this  temperature  is  maintained  for  50  or  60  minutes. 
The  crucible  is  then  allowed  to  cool  and  the  sintered  cake  can 


*  During  this  part  of  the  operation  the  heat  should  be  kept  so  low  that  am- 
monium chloride  does  not  escape.  The  latter  is  dissociated  into  ammonia  and 
hydrochloric  acid  by  the  heat,  and  the  acid  unites  with  the  calcium  carbonate  to 
form  calcium  chloride. — (Hall.) 


21 6  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

usually  be  removed  by  gently  tapping  the  inverted  crucible. 
Should  this  not  be  the  case,  it  is  digested  a  few  minutes  with 
water,  which  serves  to  soften  the  cake  so  that  it  can  be  readily 
washed  into  a  large  porcelain,  or,  better,  platinum  dish.  The 
covered  dish  is  heated  with  50-75  cc.  of  water  for  half  an  hour, 
replacing  the  water  lost  by  evaporation,  and  the  large  particles 
are  reduced  to  a  fine  powder  by  rubbing  with  a  pestle  in  the 
dish.  The  clear  solution  is  decanted  through  a  filter  and  the 
residue  is  washed  four  times  by  decantation,  then  transferred  to 
the  filter  and  washed  with  hot  water  until  a  few  cubic  centimeters 
of  the  washings  give  only  a  slight  turbidity  with  silver  nitrate.  To 
make  sure  that  the  decomposition  of  the  mineral  has  been  com- 
plete, the  residue  is  treated  with  hydrochloric  acid;  it  should 
dissolve  completely,  leaving  no  trace  of  undecomposed  mineral. 
Precipitation  oj  the  Calcium. — The  aqueous  solution  is  treated 
with  ammonia  and  ammonium  carbonate^  heated  and  filtered. 
As  this  precipitate  contains  small  amounts  of  alkali,  it  is  redis- 
solved  in  hydrochloric  acid  and  the  precipitation  with  ammonia 
and  ammonium  carbonate  is  repeated.  The  combined  filtrates 
are  evaporated  to  dryness  in  a  porcelain  or  platinum  dish,  and 
the  ammonium  salts  are  removed  by  careful  ignition  over  a 
moving  flame.*  After  cooling,  the  residue  is  dissolved  in  a  little 
water  and  the  last  traces  of  calcium  are  removed  by  the  addi- 
tion of  ammonia  and  ammonium  oxalate.  After  standing  12 
hours,  the  calcium  oxalate  is  filtered  off  and  the  filtrate  is  re- 
ceived in  a  weighed  platinum  dish,  evaporated  to  dryness,  and 
gently  ignited.  After  cooling,  the  mass  is  moistened  with  hydro- 
chloric acid  in  order  to  transform  any  carbonate  into  chloride, 
the  evaporation  and  ignition  are  repeated,  and  the  weight  of  the 
contents  of  the  dish  is  determined;  this  represents  the  amount 

*  Before  igniting,  it  is  well  to  heat  the  contents  of  the  dish  in  a  drying-oven  at 
110°.     By  this  means  there  is  no  danger  of  loss  by  decrepitation. — (Hall.) 


POTASSIUM  AND  SODIUM.  217 

of  alkali  chloride  present.  To  determine  potassium,  the  residue 
is  dissolved  in  water,  and  the  potassium  is  precipitated  as  potas- 
sium platinic  chloride,  as  described  in  §§  3,  4.  The  sodium  is 
determined  by  difference. 

2.  Hydrofluoric  Acid  Method. — Treat  i  gram  of  the  finely 
powdered  silicate  in  a  platinum  dish  with  pure  strong  hydro- 
chloric and  hydrofluoric  acids  until  decomposition  is  complete. 
It  is  best  to  add  the  hydrochloric  acid  first,  to  prevent  spattering, 
and  then  about  an  equal  amount  of  hydrofluoric  acid  and  warm 
gently.  Finally,  evaporate  to  dryness  on  the  water-bath,  then 
add  a  little  dilute  hydrochloric  acid  and  evaporate  again  to  dry- 
ness.  Dissolve  the  residue  in  hot  water,  add  5  cc.  of  a  saturated 
solution  of  barium  hydroxide,  and  heat  to  boiling  Allow  to  settle 
a  short  time  and  then  test  the  clear  liquid  with  a  little  more 
barium  hydroxide  solution  to  be  certain  that  enough  has  been 
added.  When  the  precipitation  is  complete,  filter  and  wash  well 
with  hot  water.  Heat  the  filtrate  to  boiling  and  add  a  little 
ammonia  and  ammonium  carbonate  to  complete  the  precipita- 
tion of  calcium,  barium,  etc.,  and,  after  allowing  to  stand  a  short 
time  on  the  water-bath,  filter  and  wash  the  precipitate  thoroughly 
with  hot  water.  Evaporate  the  filtrate  to  dryness  in  platinum  or 
porcelain  and  then  expel  the  ammonium  salts  by  a  heat  just 
below  redness.  Take  up  the  cool  residue  in  a  little  hot  water, 
add  a  few  drops  of  ammonia,  a  drop  or  two  of  strong  ammonium 
carbonate  solution  and  a  few  drops  of  ammonium  oxalate  solu- 
tion. After  allowing  to  stand  a  short  time  on  the  water-bath, 
set  aside  for  a  few  hours  and  then  filter,  washing  with  hot  water. 
Evaporate  the  filtrate  to  dryness  on  the  water-bath  and  heat  the 
residue  to  dull  redness  until  all  ammonium  salts  are  expelled 
and  it  has  become  nearly  or  quite  white.  Cool,  dissolve  in  a 
very  small  amount  of  water  and  filter  into  a  weighed  platinum 
dish.  Add  a  few  drops  of  hydrochloric  acid  and  evaporate  to 


2i8  TECHNICAL   METHODS   OF  ORE   ANALYSIS. 

dryness  on  the  water-bath.  Heat  the  residue  to  dull  redness, 
cool  in  a  desiccator  and  weigh  as  mixed  potassium  and  sodium 
chlorides.  Repeat  the  heating  until  a  constant  weight  is  obtained. 
Dissolve  the  chlorides  in  a  small  amount  of  water.  If  a  residue 
remains  undissolved  the  separation  must  be  repeated  until  the 
chlorides  finally  obtained  are  entirely  soluble. 

Proceed  with  the  solution  of  the  chlorides  as  described  in  3. 


SEPARATION  OF  POTASSIUM  AND  SODIUM. 

3.  Direct  Method. — It  is  assumed  that  the  two  metals  are 
in  aqueous  solution  as  chlorides  in  a  platinum  or  porcelain 
evaporating  dish,  the  weight  of  the  mixed  chlorides  being  known. 
Add  a  slight  excess  of  hydrochlorplatinic  acid  (H^PtCle)  and 
evaporate  to  dryness  at  a  low  temperature  on  a  water-bath  in 
which  the  water  is  not  boiling.  The  drying  is  to  dehydrate 
the  sodium  platinic  chloride  and  render  it  more  soluble  in  alcohol. 
It  is  a  good  plan  to  have  the  platinum  solution  contain  10  per  cent, 
of  platinum,  i.e.,  i  gram  in  every  10  cc.,  and,  in  order  to  use  the 
right  quantity  and  avoid  unnecessary  excess,  make  the  following 
calculation : 

Assume  that  the  mixed  chlorides  consist  entirely  of  NaCl. 
Call  their  weight  a.  Then  from  the  formula  Na2PtCl6  +  6H2O 
we  find  that  46.10  parts  o£  Na  require  194.6  parts  of  Pt.  46.1 
parts  of  Na  correspond  to  117  parts  of  NaCl;  therefore  we  have 
the  proportion 

1 1 7 : 194.6  =  a :  Pt  required. 

Solving  this  and  multiplying  the  result  by  10  we  arrive  at 
the  number  of  cubic  centimeters  of  platinum  solution  required. 
Always  add  0.3-0.4  cc.  in  excess. 


POTASSIUM  AND  SODIUM.  219 

It  is  necessary  to  convert  all  the  sodium  as  well  as  the  potassium 
to  the  platinum  compound,  as  otherwise  the  undecomposed 
sodium  chloride,  being  insoluble  in  absolute  alcohol,  would 
contaminate  the  potassium  platinic  chloride;  the  calculation  is 
therefore  made  as  above. 

4.  After  the  evaporation  add  to  the  cool  residue  a  few  cubic- 
centimeters  of  absolute  alcohol  (methyl  alcohol  is  the  best)  and  thor- 
oughly disintegrate  the  solid  mass  with  a  stirring-rod  or  platinum 
spatula.  Decant  the  clear  liquid  through  a  filter  moistened  with 
alcohol,  arid  then  repeat  the  stirring  with  fresh  portions  of  alcohol 
until  a  perfectly  colorless  filtrate  is  obtained  and  the  remaining 
salt  in  the  dish  is  pure  golden  yellow  with  no  intermixed  orange- 
colored  particles  of  Na2PtCle.  The  latter  compound  is  soluble 
in  the  alcohol  while  the  corresponding  potassium  salt  is  not. 
Transfer  the  washed  residue  to  the  filter,  allow  to  drain  com- 
pletely and  then  dry  in  an  air-bath  at  8o°-90°  C.  When  dry, 
carefully  transfer  as  much  of  the  precipitate  as  possible  to  a 
watch-glass.  Replace  the  filter  in  the  funnel  and  dissolve  the 
adhering  precipitate  (and  also  any  in  the  original  dish)  by  wash- 
ing with  a  little  hot  water,  receiving  the  filtrate  in  a  weighed 
platinum  dish  or  crucible.  Evaporate  the  solution  to  dryness  at 
a  low  temperature  on  the  water-bath  and  then  add  the  precipitate 
on  the  watch-glass.  Dry  the  whole  at  160°  C.  and  weigh  as 
K2PtCl6.  Multiply  this  weight  by  0.30561  to  obtain  that  of 
the  KC1.  Although  this  factor  is  correct  according  to  the  less 
recent  values  of  the  atomic  weights,  the  factor  0.30712  is  the 
correct  one  according  to  the  latest  values.  This  figure,  however, 
does  not  actually  give  results  so  near  to  the  truth  as  the  older 
factor.  This  is  due  to  the  fact  that  our  assumption  as  to  the 
formula  K^PtCle  is  not  quite  correct.  Changes  are  produced  by 
the  evaporation  which  are  compensated  for  by  the  use  of  the 
old  factor. 


220  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Having  determined  the  weight  of  the  KC1  in  the  mixed 
chlorides,  the  difference  from  the  total  weight  is  the  NaCL 

Multiply  the  weight  of  the  KC1  by  0.632  to  obtain  the  weight 
of  the  K2O. 

Multiply  the  weight  of  the  NaCl  by  0.5308  to  obtain  the 
weight  pf  the  Na2O. 

5.  Indirect  Method. — This  method  is  accurate  only  when  both 
bases  are  present  in  considerable  amount. 

The  metals  must  first  be  obtained  as  chlorides  by  one  of  the 
preceding  methods  and  the  combined  weight  noted.  Now 
determine  the  percentage  of  chlorine  in  the  mixture  (see  xi,  i) 
and  then  apply  the  following  rule: 

Subtract  47.52  from  the  percentage  of  chlorine  in  the  mixture. 
Divide  the  remainder  by  0.1307.  The  result  is  the  per  cent,  of 
sodium  chloride  in  the  mixture. 

This  rule  is  determined  as  follows:  Pure  NaCl  contains  60.59 
per  cent,  of  Cl.  Pure  KC1  contains  47.52  per  cent,  of  Cl.  The 
difference  between  the  two  percentages  is  13.07.  This  13.07 
per  cent,  excess  represents,  then,  100  per  cent,  of  NaCl,  therefore 
every  0.1307  per  cent,  above  47.52  represents  i  per  cent,  of  NaCl; 
hence  the  above  rule. 


CHAPTER   XXIV. 

SILICA. 

1.  In  the  valuation  of  ores  in  the  West  it  is  customary  to 
designate  as  "silica"  the  insoluble  residue  remaining  after  certain 
conventional  treatments  with  acids.     Precautions  are  taken  to 
remove  lead  compounds  and  sometimes  other  efforts  at  purifica- 
tion are  made,  so  that  the  final  insoluble  residue,  or  so-called 
"silica,"  shall  consist  either  of  fairly  pure  silica  or  a  mixture  of 
silica  and  undecomposed  silicates. 

2.  Insoluble  Residue  or  "  Silica  "  in  Ores,  etc.* — Weigh  0.5 
gram  of  the  ore  into  a  4-oz.  Erlenmeyer  flask.    The  choice  of 
acids  for  the  decomposition  will  depend  upon  the  apparent  nature 
of  the  ore.     Oxidized  ores,  especially  when  they  contain  much 
iron   or  manganese,   should   first   be   treated  with  hydrochloric 
acid  alone,  say  10  or  15  cc.,  and  the  mixture  warmed  very  gently 
until  decomposition  and  solution  are  as  complete  as  possible. 
Actual  boiling  should  be  avoided,  as  the  acid  is  thereby  weakened 
and  rendered  less  effective.     If  sulphides  finally  remain  undissolved 
add  a  few  cubic  centimeters  of  strong  nitric  acid  and  heat  the 
mixture  again. 

If  the  ore  is  largely  a  sulphide  it  may  frequently  be  attacked 
at  once  with  10  cc.  of  strong  nitric  acid  and  the  mixture  warmed 
gently  until  the  first  violent  action  has  somewhat  subsided.  Then 
add  5  cc.  of  strong  hydrochloric  acid  and  continue  the  warming 
to  complete  the  decomposition  if  necessary. 

*  See  21. 

221 


222  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

In  the  case  of  very  heavy  sulphides,  where  the  separated 
sulphur  after  treatment  with  nitric  acid  appears  to  be  still  impure, 
it  may  be  advisable  to  add  small  portions  of  potassium  chlorate 
from  time  to  time,  together  with  more  nitric  acid  if  necessary, 
and  continue  the  heating  until  the  sulphur  is  either  entirely 
oxidized  or  sufficiently  purified.  Then  add  5  cc.  of  strong  hydro- 
chloric acid,  very  cautiously,  to  avoid  too  violent  action  with  trie 
undecomposed  chlorate,  and  again  heat  gently. 

3.  Having  obtained  a  sufficiently  complete  decomposition  by 
any  of  the  above  methods,  or  modifications  of  them  suggested 
by  the  nature  of  the  ore  in  hand,  the  solution  is  to  be  boiled  or 
evaporated  to    complete    dryness.     This    may    be    done    either 
slowly,  by  gentle  heating  on  a  hot  plate  or  water-bath,  or  rapidly, 
by  manipulating  the  flask  over  a  small  free  flame. 

When  the  mixture  has  become  dry,  continue  the  heating 
for  5  or  10  minutes,  or  more,  at  a  temperature  of  about  150°  C., 
in  order  to  dehydrate  any  gelatinous  silicic  acid  present.  Finally, 
after  cooling  somewhat,  add  10  cc.  of  strong  hydrochloric  acid 
and  warm  until  solution  is  as  complete  as  possible.  Now  add 
40  cc.  of  water  and  about  5  grams  of  ammonium  chloride.  The 
latter  is  to  hold  lead  salts  in  solution  and  may  of  course  be  omitted 
when  no  lead  is  present.  Heat  to  boiling  and  see  that  everything 
soluble  is  properly  dissolved.  Filter  through  a  p-cm.  filter  and 
wash  well  with  hot  water.  It  is  best  either  to  have  the  water 
slightly  acidulated  with  hydrochloric  acid,  or  to  wash  at  least  once 
or  twice  with  acidulated  water,  to  remove  from  the  filter  any  insol- 
uble iron  compound  due  to  the  hydrolysis  of  ferric  chloride.  Any 
residue  adhering  in  the  flask  should  be  dislodged  with  a  rubber- 
tipped  glass  rod  and  rinsed  into  the  filter.  Ignite  and  weigh. 

4.  It  is  usually  sufficient  to  place  the  filter  and  contents,  with- 
out drying,  in  a  small  clay  "annealing-cup"  and  ignite  in  a  muffle 
or  over  a  Bunsen  burner.      When  cold  shake  and  brush  the 


SILICA.  223 

ignited  residue  upon  the  scale-pan  and  weigh.  The  weight  of 
the  filter-ash  may  ordinarily  be  neglected.  As  0.5  gram  of  ore 
was  taken,  the  weight  in  centigrams  multiplied  by  2  will  give 
the  percentage  of  "silica." 

5.  When   the   methods  above  described  fail  to  effect  a  fairly 
complete  decomposition  of  the  ore,  sulphuric  acid  may  be  tried 
in  addition.     Proceed  in  the  usual  way  with  hydrochloric  and 
nitric  acids  until  decomposition  is  about  as  complete  as  possible, 
and  then  add  5  cc.  of  strong  sulphuric  acid  and  heat  (best  over  a 
free  flame)  until  the  white  fumes  are  coming  off  copiously.     It  is 
best  to  continue  the  heating  until  most  of  the  sulphuric  acid  is 
expelled.     Cool,  dilute  with  about  40  cc.  of  water,  add  5   cc.  of 
strong  hydrochloric  acid  and  5  grams  of  ammonium  chloride,  and 
boil  to  effect  solution  of  everything  soluble.     Finally,  filter,  wash, 
ignite,  and  weigh  as  described  above. 

If  an  ore  contains  silicates  that  are  gradually  but  appreciably 
decomposed  by  acids,  it  is  evident  that  the  amount  of  insoluble 
residue  obtained  will  depend  largely  upon  the  length  of  time 
employed  in  the  treatment.  This  trouble,  which  is  inherent 
in  the  method,  does  not  often  occur  to  a  very  appreciable  extent, 
and  the  results  obtained  by  different  operators  ordinarily  agree 
fairly  well. 

6.  Barium  in   the  Insoluble   Residue.  —  If  an  ore  contains 
barium  sulphate  the  latter  will  of  course  be  found  with  the  insol- 
uble residue.     Any  soluble  barium  mineral  in  the  presence  of 
sulphates  or  sulphides  will  also  be  either  wholly  or  partly  changed 
to  sulphate  which  will  remain  behind.     When  the  insoluble  res- 
idue is  thus  contaminated  with  barium  sulphate,  it  is  customary  to 
determine  the  same  and  deduct  it.     This  may  be  done  as  follows : 

Fuse  the  mixed  residue,  after  weighing,  with  about  3  grams 
of  sodium  carbonate,  or  mixed  sodium  and  potassium  carbonates, 
best  in  a  platinum  dish.  Prolonged  fusion  is  not  necessary,  as 


224  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  object  is  simply  to  convert  the  barium  sulphate  to  carbonate. 
After  cooling,  heat  the  fused  mass  with  water  until  disintegration 
is  complete  and  then  filter  through  a  g-cm.  filter  and  wash 
thoroughly  to  remove  sulphates/  The  barium  is  left  on  the  filter  as 
carbonate,  probably  more  or  less  impure.  A  little  barium  car- 
bonate may  also  remain  adhering  to  the  platinum  dish.  Dis- 
solve the  latter  in  5  cc.  of  strong  hydrochloric  acid  diluted  with 
about  10  cc.  of  water,  and,  if  the  amount  of  carbonate  on  the 
filter  is  small,  dissolve  it  by  pouring  the  acid  mixture  (best  warmed) 
over  it  from  the  dish,  receiving  the  filtrate  in  a  large  beaker.  If 
the  quantity  of  carbonate  is  large,  rinse  it  from  the  filter  to  a 
small  beaker  and  dissolve  it  by  adding  the  acid  in  the  dish,  keep- 
ing the  beaker  covered  with  a  watch-glass  to  prevent  loss  by 
spattering.  Warm  the  solution  and  pour  it  through  the  filter  to 
dissolve  any  carbonate  remaining  thereon.  Wash  the  filter  well 
with  hot  water.  Dilute  the  filtrate  to  about  300  cc.  with  hot 
water,  heat  to  boiling  and  precipitate  the  barium  as  sulphate,  in 
the  usual  way  (consult  vn,  i),  with  dilute  sulphuric  acid.  After 
standing,  hot,  for  at  least  several  hours,  filter  off  the  barium 
sulphate,  wash  with  hot  water,  ignite,  and  weigh.  The  weight 
found,  deducted  from  that  of  the  original  mixture,  will  leave 
the  weight  of  the  insoluble  residue  required. 

7.  Treatment  of  Ores  and  Slags  that  Gelatinize  with  Acids. — 
Some  ores  and  furnace  products  are  more  or  less  completely 
decomposed  by  acids  with  the  formation  of  gelatinous  silica.  Slag 
that  has  been  suddenly  chilled  by  dipping  an  iron  bar  into  the 
molten  mass  and  then  plunging  it  with  the  adhering  slag  into 
cold  water,  may  usually  be  entirely  decomposed  by  acids.  Roasted 
ores  generally  give  gelatinous  silica.  If  such  substances  are 
treated  in  the  usual  way,  the  gelatinous  silica  is  liable  to  form 
a  cake  which  adheres  to  the  bottom  of  the  flask  and  greatly 
hinders  decomposition  by  surrounding  particles  of  the  ore  with 


SILICA.  225 

a  more  or  less  impervious  coating.  Material  of  this  class  may 
be  treated  as  follows: 

Moisten  the  0.5  gram  of  substance  in  the  flask  (a  4- inch 
porcelain  casserole  or  dish  is  better)  with  2  or  3  cc.  of  water,  and 
then  add  gradually  about  10  cc.  of  strong  hydrochloric  acid, 
stirring  or  shaking  the  mixture  at  the  same  time  to  prevent  coagu- 
lation. Cover  the  dish  with  a  watch-glass  and  heat  very  gently 
with  frequent  stirring,  until  decomposition  is  as  complete  as 
possible,  adding  a  little  nitric  acid  if  undecomposed  sulphides 
still  remain.  Finally,  remove  and  rinse  off  the  cover,  evaporate 
to  dryness  and  finish  in  the  usual  way  (3). 

In  the  case  of  chilled  slag  the  silica  thus  obtained  is  fairly 
pure.  When  there  is  much  gelatinous  silica  especial  pains  should 
be  taken  in  the  heating  after  evaporation  so  as  to  dehydrate  it 
as  thoroughly  as  possible.  In  technical  work  it  usually  suffices 
to  heat  the  dry  residue  for  half  an  hour  or  an  hour  at  a  tempera- 
ture of  about  150°  C.  (cf.  n). 

8.  "  True  Silica,"  or  "  Silica  by  Fusion."  * — These  terms,  in 
technical  work,  refer  simply  to  the  silica  obtained  by  technical 
methods  when  the  decomposition  of  the  substance  includes  a 
fusion  with  alkali  carbonate.  The  result  is  ordinarily  much 
more  accurate  as  regards  actual  silica  than  that  obtained  by 
the  usual  acid  treatment,  but  it  is  not  customary  to  follow  all 
the  requirements  of  exact  analysis.  In  the  case  of  ores  containing 
considerable  matter  soluble  in  acids,  or  constituents  undesirable 
in  the  fusion,  such  as  sulphides  and  compounds  of  reducible 
metals,  it  is  usually  best  to  give  a  preliminary  treatment  with 
acids  and  confine  the  fusion  to  the  residue  finally  obtained,  which 
may  consist  of  mixed  silica  and  undecomposed  matter.  Such  ore 


*  Insoluble  silicates,  such  as  clays,  etc.,  are  usually  decomposed  by  this  method. 
In  accurate  analyses  the  procedure  may  be  according  to  20. 


226  TECHNICAL  METHODS   OF    ORE  ANALYSIS. 

is  decomposed  and  treated,  according  to  its  nature,  precisely  as 
described  for  INSOLUBLE  RESIDUE  (2)  and  the  residue,  containing 
the  total  silica  of  the  substance,  ignited  in  a  platinum  dish  or 
crucible  to  burn  off  the  filter-paper.  It  need  not  be  weighed. 

9.  Mix  the  ignited  "insoluble  residue,"  or  0.5  gram  of  the 
finely  pulverized  ore  or  silicate,  if  no  preliminary  treatment  was 
given,  in  a  platinum  crucible  or  small  platinum  dish  with  about 
5  grams  of  sodium  carbonate,  or  a  mixture  of  3  parts  of  sodium 
carbonate  and  2  parts  of  potassium  carbonate,  which  fuses  more 
easily.      If    the  ore,  not  subjected  to  previous  acid  treatment, 
contains,  or  is  liable  to  contain,  a  small  amount  of  sulphides, 
mix  in  a  small  pinch  of  potassium  nitrate  to  insure  their  oxida- 
tion.    Heat  the  mixture  over  a  blast-lamp,  very  slowly  at  first, 
so  as  to  expel  moisture  without  mechanical  loss  of  substance. 
Raise  the  heat  very  gradually,  so  that  much  of  the  carbon  dioxide 
may  be  driven  off  without  causing  any  spattering,  before  the  mass 
has  actually  fused  to  a  liquid.     Finally  heat  strongly  to  com- 
plete fusion  of  the  mixture  and  continue  the  heating  until  bubbling 
has  practically  ceased  and  quiet  fusion  is  attained,     In  some  cases 
this  takes  from  one-half  to  one  hour.     If  a  crucible  is  used  it  is 
best  to  keep  it  covered  to  prevent  loss  from  spattering;  with  a  dish 
there  is  less  danger.     Cool  the  crucible  or  dish  and  digest  the 
fused  mass  with  hot  water.     As  a  crucible  is  too  small  to  contain 
sufficient  water,  it  is  best  to  place  it  in  a  6-inch  porcelain  dish, 
first  detaching  the  cake,   if  possible,  as  follows:    The  crucible 
having  been  chilled  quickly  by  dipping  the  bottom  in  cold  water, 
a  minute  crack  will  usually  develop  between  the  sides  of  the 
cake  and  the  crucible.     Allow  a  drop  or  two  of  water  to  fall 
into  this  crack  and  then  cautiously  heat  the  crucible  over  a  lamp. 
Under  these  conditions  the  cake  will  usually  detach  itself  with  a 
slight  "pop."     (Guiterman's  method.)     Place  the  crucible  and 
cake  in  the  evaporating-dish  and  warm  with  water  until  disin- 


SILICA.  227 

tegration  is  as  complete  as  possible.  Now  remove  and  rinse  off 
the  crucible  and  cover.  If  not  perfectly  clean  inside,  dissolve 
the  adhering  residue  with  a  little  hydrochloric  acid  and  add  the 
solution  to  the  main  portion  in  the  dish  after  the  latter  has  been 
acidified.  If  a  platinum  dish  has  been  used  instead  of  a  crucible, 
warming  in  the  dish  with  one  or  two  portions  of  water  will  usually 
suffice  for  disintegration  and  transfer  to  the  porcelain  dish.  The 
last  traces  of  residue  may  be  removed  by  the  acid  used  for  acidify- 
ing. 

10.  Cover  the  evaporating  dish  and  cautiously  add  hydro- 
chloric acid  in  excess.     It  is  not  a  good  plan  to  add  the  acid 
before  removing  the  platinum,  since  when  manganese  is  present 
chlorine  may  be  evolved  and  attack  the  platinum  if  the  latter  is 
exposed  for  any  length  of  time.     Nitric  acid  can  be  used  and 
the  danger  avoided,  but  it  is  not  so  desirable  a  solvent. 

Warm  the  mixture  in  the  dish,  and  when  the  effervescence 
has  sufficiently  subsided  remove  and  rinse  off  the  cover  and 
then  support  it  on  a  glass  triangle  placed  on  the  dish  so  as  to 
allow  a  free  circulation  of  air  over  the  liquid.  If  the  fusion 
has  been  successful  and  the  decomposition  is  complete,  practically 
everything  should  dissolve  in  the  acid  liquid  and  no  hard,  gritty, 
or  dark  particles  should  remain  in  the  bottom  of  the  dish. 

11.  The  solution  must  now  be  evaporated  to  dryness.     This 
may  be  done  on  a  water-bath  or  as  otherwise  convenient,*  except 
that  care  must  be  taken  not  to  overheat  at  the  end.     When  the 
mass  is  dry,  remove  the  triangle  and  place  it  on  top  of  the  watch- 
glass  and  the  latter  directly  on  the  dish.     This  is  to  prevent  loss 
by  any  subsequent  decrepitation.     Heat  now  over  a  radiator  or 
in  an  air-bath  at  a  temperature  of  about  150°  C.  for  30  minutes 

*  With  a  water-bath  the  operation  is  sometimes  very  tedious.  I  usually  sup- 
port the  dish  on  a  scorifier  or  triangle  placed  in  an  iron  sand-bath  or  radiator  and 
have  a  low  flame  under  the  latter. 


228  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

or  more.  The  residue  should  finally  appear  perfectly  dry  and 
powdery  under  a  glass  rod.  It  is  impossible  to  render  the  silica 
perfectly  insoluble,  so  as  to  remove  it  pure  at  one  operation,  by 
any  modification  of  the  heating,  but  for  ordinary  technical  results 
the  above  directions  will  suffice.  Too  high  a  temperature  will 
cause  a  recombination  of  some  of  the  silica  with  the  bases  present, 
and  then,  on  the  addition  of  acid,  some  of  this  silica  will  again 
be  set  free  in  a  soluble  form. 

12.  To  the  dried  mass  add  about  20  cc.  of  strong  hydro- 
chloric acid  and  allow  to  stand,  covered,  at  the  ordinary  tem- 
perature or  slightly  warmed,  for  about   10  minutes;    then  add 
about  100  cc.  of  hot  water  and  heat  to  boiling,  first  removing  and 
rinsing  off   the   cover   and   triangle.     After   boiling  a   moment, 
allow  the  silica  to  settle  and  decant  the  clear  liquid  through  a 
filter.     It  is  best  to  wash  the  silica  once  or  twice  by  decantation 
with  hot  water  and  then  transfer  it  to  the  filter  and  finish  the 
washing.     If  the  upper  edge  of  the  filter  appears  brown,  from 
the  separation  of  a  basic  ferric  compound,  due  to  hydrolysis  of 
ferric  chloride,  wash  with  warm  dilute  hydrochloric  acid  until 
clean. 

Place  the  moist  filter  and  contents  in  a  weighed  platinum 
crucible  and  ignite  until  perfectly  white.  Cool  in  a  desiccator 
and  weigh. 

13.  Testing  the  Weighed  Silica. — When  it  is  desired  to  test 
the  purity  of  the  silica  obtained,  it  may  be  done  as  follows: 
Cover  the  silica  in  the  platinum  crucible  or  dish  with  2  or  3  cc. 
of  water  to  prevent  violent  action,  and  then  add  2  or  3  drops  of 
strong  sulphuric  acid  and  3  to  5  cc.  of  pure  hydrofluoric  acid. 
Evaporate  the  mixture  as  far  as  possible  on  a  water-bath,  and 
then  heat  cautiously  over  a  small  free  flame  to  complete  dryness. 
If  there  is  a  residue  add  a  little  more  hydrofluoric  acid  and  again 
evaporate.     Repeat  this  procedure  until  no  residue  remains,  or 


SILICA.  229 

there  is  no  further  diminution  of  the  residue  obtained.  In  the 
latter  case  add  a  drop  or  two  of  strong  sulphuric  acid,  heat  to 
dryness  and  ignite  strongly  over  the  blast-lamp,  cool,  and  weigh. 
Unless  the  amount  of  residue  thus  found  is  large  it  will  usually 
be  sufficient  to  deduct  its  weight  from  that  of  the  impure  silica  to 
obtain  the  true  silica. 

Barium  sulphate  in  an  ore  would  naturally  contaminate  the 
silica.  Its  amount  could  be  determined  and  deducted  as  just 
described,  or  the  weighed  impure  silica  could  be  fused  with  alkali 
carbonate  and  the  barium  determined  as  sulphate,  as  described 
in  6.* 

14.  Determination  of  Silica  in  Ores  Containing  Fluorine.— 
Substances  containing  fluorine  will  sustain  a  loss  of  silicon  by 
volatilization  as  fluoride  if  the  solution  from  the  carbonate  fusion 
is  subjected  to  the  usual  evaporation  with  acid.     The  following 
methods  are  applicable  in  such  cases. 

15.  Seeman's     Method. t  —  Fuse    with    alkali    carbonate    as 
directed  in  9.     Extract  the  melt  with  hot  water  and  filter  from 
the  insoluble  residue.     Any  barium  present  will  remain  with  the 
residue  as  carbonate.     Make  the  filtrate  faintly  acid  with  hydro- 
chloric acid  and  then  add  an  excess  of  a  solution  of  mercury 
ammonium  carbonate.     Evaporate  the  mixture  to  dryness,  add 
water  to  the  residue  and  again  evaporate  to  dryness.     Take  up 
the  residue  in  hot  water.     It  is  easily  filtered  and  washed  and 
may  be  directly  ignited  and  weighed  to  obtain  the  anhydrous 
silica. 

The  mercury-ammonium  carbonate  may  be  prepared  by 
adding  to  a  quantity  of  mercuric  oxide  a  sufficient  excess  of  a 

*  A  more  common  method  at  western  srnelting-works  is  to  filter  the  aqueous 
solution  of  the  melt  of  the  original  fusion  b3fore  acidifying.  The  barium  is  thus 
practically  all  removed  as  carbonate  at  this  point. 

f  F.  Seeman,  Zeit.  f.  anal.  Chem.,  LXIV,  343-387. 


230  TECHNICAL  METHODS  OF   ORE   ANALYSIS. 

cold  saturated  solution  of  ammonium  carbonate  to  form  a  clear 
solution. 

16.  Method  of  Berzelius. — Thoroughly  extract  the  melt  from 
the  alkali  carbonate  fusion  (9)  with  hot  water  and  filter  from 
the    insoluble    residue.     (Any    barium    will    remain    behind    as 
carbonate.)     To  the  filtrate  add  about  4  grams  of  solid  ammo- 
nium carbonate,  heat  for  some  time  at  about  40°  C.  and  then 
allow  to  stand  over  night.     Filter  off  the  precipitate  and  wash 
with  water  containing  ammonium  carbonate.     Reserve  the  silica 
thus  obtained. 

Some  silica  still  remains  in  the  filtrate.  To  recover  this,  add 
to  the  solution  i  or  2  cc.  of  ammoniacal  zinc  oxide  solution  (made 
by  dissolving  moist  zinc  oxide  in  ammonia  water),  boil  until  the 
ammonia  is  all  expelled  and  then  filter  off  the  precipitate  of  zinc 
silicate  and  oxide  and  wash  with  water.  Spread  out  the  filter 
on  a  watch-glass,  and,  with  a  jet  from  the  wash- bottle,  rinse  as 
much  of  the  precipitate  as  possible  into  an  evaporating-dish. 
Pour  a  little  dilute  hydrochloric  acid  over  the  filter  and  any 
remaining  residue,  letting  it  run  into  the  dish,  then  burn  the 
filter  and  add  the  ash.  Add  a  little  more  hydrochloric  acid  to 
the  contents  of  the  dish,  if  necessary  to  decompose  the  precipitate, 
and  then  evaporate  on  the  water-bath  and  separate  the  silica  as 
usual  (n).  Filter  off  this  silica  and  reserve  it. 

The  insoluble  part  of  the  melt  may  contain  silica.     Dissolve 
it  in  hydrochloric  acid  and  separate  the  silica  by  evaporation 
as  usual.     (Any  barium  will  pass  into  the  filtrate  as  chloride.) 
Finally  ignite  and  weigh  all  three  silica  precipitates  together. 

17.  Decomposition  of  Silicates  by  the  Lead   Oxide  Method 
of  Jannasch. — This  method  is  applicable  in  the  case  of  pure 
silicates  and  admits  of  determination  of  the  alkalies  in  the  same 
portion.     Pure  lead  oxide  is  required,  but  as  the  commercial 
article  is  not  safe,  it  is  best  to  use  the  carbonate,  which  is  con- 


SILICA.  231 

verted  into  the  oxide  by  ignition.  It  may  be  prepared  as  follows: 
To  a  boiling  solution  of  lead  acetate  add  the  theoretical  amount 
of  ammonium  carbonate.  Wash  the  precipitated  lead  carbonate 
several  times  by  decantation  with  hot  water,  then  transfer  it 
to  a  hardened  filter  (to  avoid  contamination  with  loosened 
fibers),  wash  completely  and  allow  to  drain  thoroughly,  or  better, 
use  suction.  Carefully  remove  from  the  filter  and  dry  com- 
pletely in  a  porcelain  dish  on  the  water-bath. 

1 8.  Mix  i  gram  of  the  very  finely  powdered  substance  with 
10-12  grams  of  lead  carbonate.  Place  the  carbonate  in  the 
crucible  first,  then  add  the  weighed  substance  and  mix  very 
thoroughly  with  a  platinum  spatula.  Cover  the  crucible  and 
heat  gently,  below  the  fusing-point  of  the  mixture,  for  15  or  20 
minutes,  to  expel  most  of  the  carbon  dioxide.  Now  heat  more 
strongly,  being  careful  to  have  a  non-luminous  oxidizing  flame, 
until  the  fusion  is  complete  and  keep  it  at  this  temperature  for 
10  or  15  minutes.  Only  the  lower  third  of  the  crucible  should 
be  heated  to  redness.  Cool  the  crucible  quickly  by  dipping 
the  bottom  in  hot  water,  then  place  it,  together  with  the  cover, 
in  a  platinum  dish  and  cover  with  hot  water.  After  adding 
sufficient  strong  nitric  acid  to  insure  solution  of  the  lead,  heat 
on  a  water-bath  until  disintegration  is  complete.  Remove  the 
crucible  and  cover  when  the  adhering  portions  of  the  melt  have 
dissolved  or  separated  therefrom.  To  assist  in  the  disintegra- 
tion stir  the  mixture  frequently  and  break  up  hard  lumps  as 
much  as  possible.  Only  slightly  colored  flocks  of  silicic  acid 
should  finally  remain  floating  in  the  liquid.  Now  evaporate  to 
complete  dryness.  Moisten  the  dry  mass  with  strong  nitric 
acid  and  again  evaporate  to  dryness.  Add  20  cc.  of  strong 
nitric  acid  to  the  dry  residue,  allow  to  stand  15  minutes  and 
then  add  100  cc.  of  water.  Heat  the  mixture  for  20  minutes 
on  the  water-bath  and  then  filter.  Wash  the  silicic  acid  first 


232  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

with  hot  water  acidulated  with  nitric  acid,  and  then  with  pure 
hot  water.     Ignite  and  weigh  in  the  usual  manner. 

19.  Common  Errors  in  the  Determination  of  Silica. — Under 
this  heading  Dr.  Hillebrand  has  published  an  exhaustive  paper 
in  Vol.  XXIV  of  the  Journal  of  The  American  Society.  While 
the  technical  chemist,  working  by  conventional  methods,  might 
regard  his  findings  as  of  minor  importance,  they  should  never- 
theless always  be  borne  in  mind.  They  are  as  follows: 

1.  Silica  cannot  be  rendered  wholly  insoluble  by  any  number 
of  evaporations  with  hydrochloric  acid  when  followed  by  a  single 
filtration,  no  matter  what  temperature  may  be  employed.     Two 
or  more  evaporations  alternating  with  nitrations  are  necessary  to 
secure  satisfactory  results.* 

2.  The  generally  accepted  view  that  silica  passing  into  the 
filtrate  is  wholly  thrown  down  by  ammonia  or  sodium  acetate 
in  presence  of  much  alumina  or  iron  is  incorrect. 

3.  Silica  is  appreciably  soluble  in  melted   potassium  pyro- 
sulphate,  and  consequently,  when  silicious  oxides  of  iron  and 
aluminum  obtained  in  analysis  are  thus  fused,  their  silica  con- 
tents are  only  in  small  part  left  undissolved  when  the  fused  mass 
is  taken  up  with  water  or  acid.     These  last  two  sources  of  error 
may  be  avoided  by  separating  all  silica  at  the  start  as  above. 

4.  The  need  of  long  blast  ignition  of  the  silica  in  order  to 
get  the  correct  weight  is  proved;  continual  loss  of  weight  being 
invariably  observed  for  30  minutes  or  more. 

20.  Accurate  Method  for  Silica. — Treadwell,f  for  an  accu- 
rate   silica    determination,    directs    as    follows:     Evaporate    the 


*  Hillebrand  (private  communication)  says:  "Where  I  have  fused  a  gram 
of  rock  (silicate)  with  4-6  grams  of  sodium  carbonate,  I  always  recover  about  3 
milligrams  of  silica  from  the  iron  and  alumina,  even  after  two  evaporations  and 
nitrations." 

t  Anal.  Chemistry,  Hall,  2d  Ed.,  Vol.  II,  p.  445. 


SILICA.  233 

dilute  hydrochloric  acid  solution  of  the  residue  after  the  fusion,  or 
the  original  material  if  entirely  decomposed  by  acid,  in  a  porce- 
lain dish,  to  dryness  on  the  water-bath.*  Stir  frequently  until 
the  residue  is  obtained  as  a  dry  powder.  Moisten  this  with 
strong  hydrochloric  acid,  cover  the  dish  and  allow  to  stand  at 
least  20  minutes  at  the  ordinary  temperature,  to  insure  the 
changing  to  chlorides  of  any  basic  salts  or  oxides  formed  during 
the  evaporation.  Then  add  100  cc.  of  water,  heat  to  boiling, 
allow  the  silicic  acid  to  settle  and  decant  the  clear  liquid  through 
a  filter  supported  upon  a  platinum  cone  in  a  funnel.  Wash  the 
residue  three  or  four  times  by  decantation  with  hot  water,  then 
transfer  to  the  filter  and  wash  with  hot  water  until  free  from 
chloride.  If  the  silicic  acid  is  not  perfectly  white,  but  brownish 
from  basic  ferric  salt,  drop  strong  hydrochloric  acid  around  the 
upper  edge  of  the  filter  and  immediately  wash  it  down  with  a 
stream  of  hot  water.  Repeat  this  until  the  filtrate  comes  through 
perfectly  colorless.  Finally,  dry  the  precipitate  by  suction, 
place  it  in  a  platinum  crucible  and  set  it  aside  for  the  time  being. 
The  separation  of  the  silica  is  now  by  no  means  quantitative; 
as  much  as  5  per  cent,  of  the  total  amount  may  remain  in  the 
filtrate.  To  remove  this,  evaporate  the  solution  once  more  on 
the  water-bath  to  dryness,  keep  at  this  temperature  for  i  or  2 
hours  (or  more),  moisten  with  a  few  cubic  centimeters  of  con- 
centrated hydrochloric  acid  and  allow  to  stand  not  more  than 
15  minutes.  Too  long  a  contact  with  the  acid  at  this  point  will 
cause  some  of  the  silicic  acid  to  go  into  solution.  Add  hot  water, 
filter  the  residue  through  a  new,  and  correspondingly  small, 
filter  and  wash  with  hot  water. 

The  amount  of  silicic  acid  now  remaining  in  the  filtrate  should 

*  This  is  sometimes  a  very  tedious  operation.  Hillebrand  says  of  the  drying: 
"  It  can  safely  be  done  at  temperatures  higher  than  that  of  the  water-bath."  — 
Private  communication. 


234  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

not  exceed  0.15  per  cent,  of  the  total  quantity  and  may  usually 
be  neglected.  It  can  be  removed,  however,  by  a  third  evapora- 
tion to  dryness. 

The  filters  containing  the  silica  are  ignited  wet  in  a  platinum 
crucible,  and  finally  over  the  blast-lamp,  and  weighed. 

Treadwell  further  remarks:  In  order  to  make  the  separation 
of  silicic  acid  quantitative  it  has  been  proposed  to  heat  the  residue 
obtained  by  evaporation  at  no°-i2o°C.  It  has  been  found, 
however,  that  nothing  is  gained  by  this  practice,  as  some  silicic 
acid  is  obtained  in  the  filtrate  and  the  deposited  silicic  acid  is 
less  pure  than  when  dried  on  the  water-bath.  When  magnesia 
was  present  more  silicic  acid  was  found  in  the  filtrate  after  ignit- 
ing at  280°  than  when  dried  on  the  water-bath.  This  is  due  to  the 
fact  that  magnesia  formed  by  hydrolysis  reunites  with  the  silica 
to  form  magnesium  silicate,  and  the  latter  is  decomposed  by 
hydrochloric  acid  with  the  formation  of  soluble  silicic  acid.  It 
is,  therefore,  not  advisable  to  attempt  to  dehydrate  the  silica  at  3. 
temperature  higher  than  that  of  the  water- bath. 

21.  Methods  in  Use  at  the  Colorado  Plants  of  the  American 
Smelting  and  Refining  Co.  for  the  Determination  of  Insoluble 
Matter  in  Ores,  etc.* — The  methods  used  in  the  different  labora- 
tories may  differ  somewhat  in  unimportant  details,  but  in  general 
are  as  follows: 

Unless  there  is  some  special  reason  otherwise,  one-half  gram 
is  taken  in  all  cases  for  the  determination. 

Sulphides. 

Treat  in  No.  o  beaker,  or  small  casserole,  with  strong  nitric 
acid,  7-10  cc.  Heat  gently  until  strong  action  has  ceased. 
Evaporate  to  dryness  and  bake  until  free  from  acid.  Cool,  add 

*  Western  Chemist  and  Metallurgist,  III,  120. 


SILICA.  235 

about  20  cc.  hydrochloric  acid  (i  part  acid  and  i  part  water) 
and  heat  until  solution  is  as  complete  as  possible.  Filter,  wash 
first  with  hot  dilute  hydrochloric  acid,  then  hot  water.  Ignite 
and  weigh. 

.  Occasionally  some  ores  high  in  zinc  or  lead  sulphide  may  be 
treated  to  advantage,  first  with  hydrochloric  acid,  and  then 
following  as  above,  but  the  result  should  be  the  same  in  either 
case  if  properly  carried  out. 

Oxidized  Ores  in  General. 

Treat  with  strong  hydrochloric  acid,  7-10  cc.  Boil  until  dis- 
solved; add  a  little  nitric  acid  (0.5  cc.  are  usually  plenty);  evapo- 
rate to  dryness  and  bake  to  the  complete  expulsion  of  acid 
fumes.  Cool;  take  up  with  hydrochloric  acid  and  proceed  as 
with  sulphides. 

With  some  ores  containing  carbonaceous  matter,  it  may  be 
necessary  to  bake  for  a  long  time,  as  such  residues  often  hold 
acid  very  tenaciously. 

Manganese  Oxides. 
Nitric  acid  is  omitted  entirely  with  these. 

Leady  Oxide  Ores. 

Some  of  these  usually  yield  gelatinous  silica  and  must  be 
carefully  dehydrated  at  not  too  high  a  temperature. 

Oxidized  Material  Which  has  been  Strongly  Ignited. 

Digest  with  hydrochloric  acid  without  boiling  at  first,  then 
evaporate  nearly  to  dryness,  add  a  few  drops  of  nitric  acid  and 


236  TECHNICAL   METHODS    OF   ORE  ANALYSIS. 

evaporate  to  complete  dryness.  Occasionally  it  may  be  neces- 
sary to  repeat  this  treatment,  which  is  a  matter  of  individual 
judgment.  Finally  bake  to  complete  expulsion  of  acid  and 
proceed  as  before. 

Roasted  Ores,  Acid  Works'  Residues,  Etc. 
Digest  with  hydrochloric  acid,  without  boiling,  until  oxidized 
portion  is  dissolved,  add  2-3  cc.  of  nitric  acid,  boil  to  decompose 
sulphides,  evaporate  to  dryness  and  proceed  as  before. 

Ores  or  Products  Containing  Magnetite 

Some  mixed  oxidized  and  sulphide  ores,  and  also  often  furnace 
mattes,  contain  magnetite.  When  this  is  known  or  suspected, 
the  material  is  treated  as  above  under  "Roasted  Ores,  etc.," 
except  that  nitric  acid  in  larger  quantity  may  sometimes  be 
necessary. 

Barium  Sulphate  Ores. 

Treat  with  10  cc.  hydrochloric  acid  (i  part  acid  and  i  part 
water),  boiling  a  few  minutes,  add  4-5  cc.  nitric  acid,  and  after 
action  has  ceased  evaporate  to  dryness.  Bake  and  proceed  as 
usual. 

After  total  insoluble  is  weighed,  fuse  with  sodium  carbonate 
or  mixed  carbonates,  digest  the  melt  with  water  until  disintegrated, 
filter  and  wash.  Wash  out  the  fusion  crucible  with  3-5  cc. 
hydrochloric  acid  (i  :  i)  and  with  this  dissolve  the  residue  on 
the  filter,  being  careful  that  the  residue  is  all  dissolved  and  the 
filter  washed  clean.  Precipitate  the  barium  in  boiling  solution 
with  a  slight  excess  of  dilute  sulphuric  acid,  and  allow  to  stand 
at  least  2  hours  before  filtering.  The  barium  sulphate  so 
obtained  is  deducted  from  the  total  insoluble  to  give  the  insoluble 
residue. 


SILICA.  237 

General  Notes. 

Care  must  be  taken  to  insure  the  removal  of  all  lead  salts  from 
the  insoluble  residue.  Filtrations  should  be  conducted  rapidly 
and  with  hot  solutions,  in  which  case  washing  with  hot  dilute 
hydrochloric  acid  is  perfectly  safe.  However,  washing  with  hot 
ammonium  chloride  or  acetate  solution  is  often  used  and  has  no 
objections.  This  removal  of  lead  needs  special  care  in  barium 
sulphate  ores,  as  this  latter  seems  to  render  the  complete  solution 
of  the  lead  salts  more  difficult. 

The  use  of  the  Baker  and  Adamson  No.  A  filter  paper  is 
recommended  as  less  likely  than  most  papers  to  allow  fine  pre- 
cipitates to  pass  through. 


CHAPTER  XXV. 

SULPHUR. 

i.  Method  for  Ores,  etc.,  Giving  Total  Sulphur.* — Prepare  an 
intimate  mixture  of  i  part  of  dry  sodium  carbonate  and  4  parts 
of  zinc  oxide.  Weigh  0.5  gram  of  the  ore  into  a  small  platinum 
or  porcelain  dish,  add  3  grams  of  the  above  mixture  and  mix 
thoroughly,  best  by  rubbing  together  with  a  small  agate  pestle. 
Cover  with  2  grams  more  of  the  zinc  oxide  mixture. f  If  a  plat- 
inum dish  is  used,  set  it  in  a  hole  in  a  piece  of  asbestos-board 
(to  exclude  sulphur  coming  from  the  gas),  cover  partially 
with  a  piece  of  thin  asbestos-board,  and  heat  over  a  Bunsen 
burner  to  bright  redness  for  about  twenty  minutes.  If  a  porcelain 
dish  is  used  it  is  difficult  to  attain  the  proper  heat  with  a  Bunsen 
burner,  and  it  is  best  to  heat  it  in  a  muffle  or  over  a  suitably 
adjusted  blast-lamp.  Allow  to  cool  and  transfer  the  mass  to  a 
25o-cc.  beaker.  Rinse  out  the  dish  thoroughly  with  hot  water 
and  make  up  the  bulk  in  the  beaker  to  about  50  cc.  Heat  the 
mixture  to  boiling,  stirring  well,  and  then  filter  through  an 
1 1 -cm.  filter  and  wash  the  residue  at  least  ten  times  with  hot 
water.  Receive  the  filtrate  in  a  6oo-cc.  Erlenmeyer  flask.  Add 
a  drop  of  phenolphthalein  solution  as  indicator,  make  just  acid 
with  strong  hydrochloric  acid,  and  then  add  4  cc.  in  excess.  Dilute 
the  solution  to  about  400  cc.  with  hot  water,  heat  to  boiling  and 
precipitate  the  sulphur  with  barium  chloride,  as  described  in  6. 
For  ordinary  technical  work  I  do  not  follow  all  of  Folin's  direc- 

*  The  use  of  the  zinc  oxide  mixture  is  described  by  Ebaugh  and  Sprague,  Jour. 
Am.  Chem.  Soc.,  XXIX,  1475. 

fSee  Note,  page  245.  238 


SULPHUR.  239 

tions.  Continue  as  follows :  After  adding  the  barium  chloride,  as 
described,  to  the  boiling  solution,  allow  the  mixture  to  stand,  hot, 
until  the  liquid  above  the  precipitate  has  become  perfectly  clear — • 
perhaps  an  hour.  Filter  through  a  double  i  i-cm.  filter.  No  appreci- 
able amount  of  barium  sulphate  should  run  through.  Unless,  how- 
ever, the  filtrate  appears  practically  clear,  always  filter  a  second 
time,  which  will  usually  suffice.  Wash  the  precipitate  ten  times 
with  hot  water.  Transfer  the  moist  filter  and  precipitate  to  a 
clean  smooth  "annealing-cup"  and  ignite,  with  free  access  of  air, 
over  a  Bunsen  burner,  or  in  a  muffle,  at  a  gentle  heat.  A  high 
heat,  such  as  that  of  a  blast-lamp,  is  neither  necessary  nor  desirable. 
The  ignited  barium  sulphate  should  be  perfectly  white.  Cool  in 
desiccator,  transfer  to  the  scale-pan  by  tapping  and  brushing 
with  a  camel's-hair  brush,  and  weigh.  Multiply  the  weight  of 
the  barium  sulphate  by  0.1373  to  obtain  the  weight  of  the  sulphur. 

A  platinum  or  porcelain  crucible  may,  of  course,  be  used  for 
the  ignition  of  the  barium  sulphate  instead  of  an  annealing-cup. 

It  is  best  to  run  a  blank,  once  for  all,  with  all  the  reagents 
employed,  and  always  deduct  for  any  sulphur  thus  found. 

It  is  usually  unnecessary  to  test  the  filtrate  from  the  barium 
sulphate  with  more  barium  chloride,  unless  the  precipitate  is 
large  in  amount,  or  the  percentage  of  sulphur  found  approxi- 
mates the  total  amount  that  10  cc.  of  the  barium  chloride  solution 
are  capable  of  precipitating  (6). 

2.  Acid  Method  for  Ores  (Not  Giving  the  Sulphur  of  Barium 
Sulphate). — Treat  0.5  gram  of  the  ore  in  an  8-oz.  flask  with 
10  cc.  of  strong  nitric  acid.  Heat  very  gently  until  the  red  fumes 
have  somewhat  abated,  and  then  add  potassium  chlorate  in 
small  portions  at  a  time  (say  0.2-0.3  gram),  until  any  free  sul- 
phur that  has  separated  is  entirely  oxidized  and  dissolved.  The 
acid  should  not  be  boiled  violently,  as  this  would  unnecessarily 
weaken  it.  On  the  other  hand,  it  is  best  not  to  allow  it  simply 


240  TECHNICAL  METHODS    OF  ORE  ANALYSIS. 

simmer,  as  the  explosive  gases  from  the  decomposing  chlorate 
may  then  collect  in  the  flask  and  produce  annoying,  although  not 
dangerous,  explosions.  When  the  sulphur  has  entirely  disappeared 
the  solution  should  be  boiled  to  complete  dryness.  This  oper- 
ation may  be  hastened  by  manipulating  the  flask  over  a  free 
flame.  After  cooling,  add  5  cc.  of  strong  hydrochloric  acid. 
This  should  be  done  cautiously  to  avoid  a  too  violent  reaction 
with  the  undecomposed  potassium  chlorate  that  may  be  present. 
If  iron  oxide,  etc.,  still  remains  undissolved,  gently  heat  the  hydro- 
chloric acid  mixture  until  solution  is  as  complete  as  possible, 
adding  more  acid  if  necessary.  Finally,  boil  to  dryness,  then 
add  5  cc.  more  of  the  hydrochloric  acid  and  again  boil  to  dry- 
ness.  This  is  to  decompose  nitrates  and  expel  all  nitric  acid. 
Take  up  once  more  in  5  cc.  of  hydrochloric  acid  and  dilute  with 
about  100  cc.  of  cold  water.*  Make  alkaline  with  ammonia 
and  then  add  10  cc.  of  a  saturated  solution  of  ammonium  car- 
bonate. This  latter  is  to  convert  any  lead  sulphate  to  carbonate 
and  thus  render  the  combined  SOs  soluble,  as  ammonium  sul- 
phate. Heat  to  boiling,  allow  the  ferric  hydroxide,  etc.,  to  settle, 
and  then  filter  and  wash  very  thoroughly  with  hot  water,  receiving 
the  filtrate  in  a  6oo-cc.  Erlenmeyer  flask.  Proceed  with  the 
filtrate  as  described  in  i. 

3.  Modification  of  the  Acid  Method  for  Ores  Containing 
Barium  Sulphate. — As  barium  sulphate  remains  practically 
unaffected  by  the  above  acid  treatment,  any  sulphur  thus  com- 
bined in  an  ore  will  require  another  method  for  its  solution. 
When  the  total  sulphur  is  required  in  ores  containing  barium 
sulphate,  the  procedure  may  either  be  according  to  i,  or  the  acid 
method  may  be  modified  as  follows:  Begin  the  analysis  accord- 
ing to  2,  and  proceed  as  described  until  all  nitric  acid  has  been 

*  If  the  solution  is  hot  when  made  alkaline  with  ammonia,  some  basic  ferric 
sulphate  is  liable  to  separate. 


SULPHUR.  241 

expelled  and  the  residue  has  been  taken  up  for  the  last  time  in 
5  cc.  of  hydrochloric  acid.  Now  dilute  with  about  30  cc.  of 
water,  add  5  grams  of  pure  ammonium  chloride  and  heat  to 
boiling.  The  ammonium  chloride  is  to  hold  any  lead  in  solution. 
Filter  and  wash  with  hot  water.  Reserve  the  nitrate,  which 
contains  all  the  sulphur  that  yielded  to  the  acid  treatment.  Ignite 
the  insoluble  residue,  containing  the  barium  sulphate,  in  a  plati- 
num dish  or  crucible  to  burn  off  the  filter-paper.  When  cool, 
add  a  little  sodium  carbonate,  or  mixed  sodium  and  potassium 
carbonates,  and  fuse  to  decompose  the  barium  sulphate  and 
form  soluble  alkali  sulphate.  A  prolonged  fusion  is  not  necessary. 
Cool,  take  up  the  mass  in  hot  water,  warming  until  thoroughly 
disintegrated,  and  then  filter  and  wash  with  hot  water.  Make 
the  filtrate  slightly  acid  with  hydrochloric  acid,  keeping  the 
beaker  covered  to  avoid  loss  by  spattering,  and  then  add  to  it 
the  reserved  filtrate.  The  united  filtrates  are  now  cooled  (cf. 
foot-note,  p.  240),  made  alkaline  with  ammonia,  ammonium  car- 
bonate added,  and  the  determination  proceeded  with  in  the  usual 
way. 

4.  Waring's  Method  for  Sulphur  in  Ores,  etc.* — To  i  part 
of  the  ore,  ground  impalpably  fine,  add  i  part  of  potassium 
chlorate  and  2  parts  of  sodium  carbonate.  Mix  and  grind 
thoroughly  together  in  an  agate  mortar.  Add  4  to  6  parts  of 
pure  precipitated  manganese  dioxide  and  again  grind  together. 
Prepare  a  platinum  or  porcelain  crucible  to  receive  the  mixture 
by  lining  its  sides  and  bottom  with  magnesium  oxide  with  the 
aid  of  the  agate  pestle  (upper  end).  Pour  and  brush  the  mixture 
into  the  cavity  and  cover  with  a  little  additional  manganese 
dioxide.  Heat  the  crucible  very  gradually  to  a  moderate  red 
heat  (750°  or  8co°  C.),  and  maintain  this  temperature  for  15  or 

*  Communicated  by  W.  Geo.  Waring. 


242  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

20  minutes.  When  cold,  invert  the  crucible  over  a  casserole 
or  beaker  so  the  calcined  but  yet  pulverulent  mass  may  drop  out. 
Add  40  or  50  cc.  of  hot  water,  boil  thoroughly,  allow  to  settle 
and  decant  through  a  filter.  Repeat  the  washing  by  decantation 
three  or  four  times  and  finally  transfer  the  residue  to  the  filter 
and  wash  with  hot  water.  A  few  drops  of  bromine  water  may 
be  added  with  the  last  washing.  Slightly  acidify  the  filtrate  with 
hydrochloric  acid,  heat  to  boiling  and  precipitate  with  hot  barium 
chloride  solution. 

The  essential  feature  is  the  intimate  mixture  by  grinding. 
If  this  is  not  thoroughly  done,  a  little  sulphur  may  sometimes  be 
found  in  the  residue  upon  treatment  with  hydrochloric  acid,  etc. 
The  residue  should  always  be  tested  in  this  way,  although  Waring 
states  that  he  has  never  found  it  to  contain  sulphur  except  when 
the  grinding  was  omitted  and  the  reagents  and  mineral  mixed 
merely  with  a  spatula,  or,  in  some  cases,  when  potassium  nitrate 
was  used  instead  of  chlorate.  Generally,  the  nitrate  may  be 
used  successfully.  The  reagents  should  be  tested  by  a  blank 
and  the  sulphur  found  deducted.  The  magnesium  oxide  serves 
two  purposes, — preventing  adhesion  of  particles  of  the  assay 
to  the  crucible,  and  also  preventing  silicic  acid  from  going  into 
the  aqueous  solution  and  producing  erroneous  results.*  Waring 
states  that  no  other  method  he  has  tried  yields  such  accurate 
results. 

5.  Method  for  Roasted  Ores,  and  Ores  Containing  Much 
Copper. — By  the  wet  method,  some  of  the  sulphur  of  roasted  ores 
is  liable  to  escape  as  hydrogen  sulphide.  Also,  if  the  solution  to 
which  ammonia  is  added  contains  much  copper,  some  of  the 
latter  is  liable  to  separate  as  a  basic  sulphate,  and,  furthermore, 
the  copper  in  the  filtrate  will  contaminate  the  barium  sulphate. 

*  Hillebrand  states  that  silicic  acid   in  dilute  solution  is  not  precipitated  with 
the  barium  sulphate.     Bulletin  176  of  the  U.  S.  Geological  Survey  (1900),  p.  106. 


SULPHUR  243 

Both  of  these  sources  of  error  may  be  avoided  as  follows:  Fuse 
0.5  gram  of  the  ore  in  a  large  porcelain  crucible  with  25  grams 
of  a  mixture  of  6  parts  sodium  carbonate  and  i  part  potassium 
chlorate  (Bockmann's  method).  Contamination  with  sulphur  of 
illuminating-gas  is  best  avoided  by  placing  the  crucible  within  a 
hole  in  a  piece  of  asbestos  board.  Heat  gently  at  first,  and  finally 
until  the  evolution  of  oxygen  ceases.  Cool,  extract  with  water 
and  filter,  washing  thoroughly  with  hot  water.  Acidify  the  filtrate 
with  hydrochloric  acid  and  continue  as  described  in  i. 

6.  Notes  on  the  Precipitation  of  Barium  Sulphate. — Accord- 
ing to  a  series  of  most  careful  tests  by  Otto  Folin,*  most  sul- 
phate precipitations,  carried  out  by  the  usual  methods,  are 
liable  to  considerable  errors,  which  may  be  either  losses  or  gains. 
Folin  shows  that  accurate  results  may,  in  ordinary  cases,  be 
obtained  as  follows: 

Have  the  barium  chloride  solution  of  10  per  cent,  strength. 
Only  a  slight  excess  is  necessary,  and  it  should  be  allowed  to 
drop  through  a  capillary  opening  at  the  bottom  of  a  small  funnel, 
so  that  10  c.c.  will  run  through  in  from  2  to  10  minutes. 

The  precipitation  is  most  conveniently  made  in  an  Erlen- 
meyer  flask,  with  the  dropping-funnel  placed  in  the  neck.  The 
sulphate  solution  should  be  hot  and  contain  an  excess  of  from 
i  to  4  c.c.  of  strong  hydrochloric  acid  per  1 50  c.c.  of  solution.  The 
sulphates  present  should  not  yield  over  0.200  gram  of  barium 
sulphate  per  100  c.c.  After  the  addition  of  the  barium  chloride, 
allow  to  stand  until  cold  and  then  filter,  washing  with  cold 
water.  It  is  best  to  use  a  porcelain  Gooch  crucible  for 
the  filtration,  as  when  paper  is  used  there  is  an  appreciable 
mechanical  loss  in  the  subsequent  ignition.  Even  with  a  Gooch 
crucible  there  must  be  certain  precautions  in  the  ignition  to  avoid 

*  Jour,  of  Biological  Chemistry,  i,  131. 


244  TECHNICAL  METHODS   OF    ORE  ANALYSIS. 

loss.  Have  the  crucible  covered  and  protect  the  bottom  by  stand- 
ing the  crucible  on  the  cover  of  a  platinum  crucible  placed  on  a 
triangle.  Ten  minutes  will  suffice  for  the  ignition  in  the  absence 
of  organic  matter. 

If  a  paper  filter  is  used,  mechanical  loss  will 'occur  during 
the  ignition,  in  spite  of  every  precaution.  The  loss  may  be  re- 
duced to  a  minimum  by  regulating  the  heat  at  the  beginning  so 
that  the  filter  will  char  slowly  without  taking  fire.  This  method 
will  suffice  for  ordinary  technical  work. 

10  cc.  of  a  10  per  cent,  solution  of  barium  chloride  will 
precipitate  0.1416  gram  of  sulphur,  or,  on  the  basis  of  0.5  gram 
of  ore,  28.32  per  cent.  On  the  same  basis  the  precipitating 
solution  should  not  contain  more  than  5.6  per  cent,  of  sulphur 
per  100  cc.  For  an  ore  containing  20  per  cent,  of  sulphur  the 
solution  should  be  diluted  to  about  400  cc.  and  have  an  excess 
of  4-5  cc.  of  strong  hydrochloric  acid.  When  more  than  this 
amount  of  sulphur  is  possibly  present,  it  is  better  to  take  less 
than  0.5  gram  of  the  ore  rather  than  largely  increase  the  volume 
of  the  solution  for  precipitation. 

7.  Determination  of  Sulphur  in  Liquid  Fuel.* — Treat  2  or 
3  grams  of  the  fluid  with  4  cc.  of  fuming  nitric  acid  in  a  large 
platinum  crucible  covered  with  a  watch-glass.  When,  after 
several  hours,  the  reaction  in  the  cold  has  ceased,  heat  the 
crucible  on  a  gently- warmed  water- bath.  When  the  mass  has 
quieted  down  remove  the  cover  and  continue  the  heating  until 
the  material  is  dry.  Now  add  6-8  grams  of  a  mixture  of  calcined 
sodium  carbonate  (free  from  silica  and  sulphate)  with  2  parts  of 
potassium  nitrate  and  heat  over  a  rosette- burner,  stirring  with  a 
platinum  rod  as  soon  as  the  mass  softens.  Cover  with  more  of 
the  nitrate  mixture  and  continue  the  heating  until  the  com- 

*  A.  Goetzl.  Zeit.  f.  angew.  Chem.,  1905,  No.  30,  p.  1528. 


SULPHUR.  245 

bustion  is  complete.  Allow  to  cool,  dissolve  the  melt  in  hot 
water  and  transfer  to  a  beaker.  Make  slightly  acid  with  hydro- 
chloric acid,  dilute  sufficiently,  heat  to  boiling  and  precipitate 
with  barium  chloride  in  the  usual  manner,  finally  igniting  and 
weighing  the  BaSO4. 


Note  to  Paragraph  i. — There  should  always  be  present  at 
least  twice  as  much  sodium  carbonate  as  would  be  required  to 
combine  with  the  sulphur,  arsenic,  etc.,  in  the  ore. 


CHAPTER    XXVI. 
TIN. 

THE  following  is  the  best  method  with  which  I  am  acquainted 
for  the  technical  determination  of  tin  in  ores,  etc.  It  is  very 
rapid  (usually  requiring  less  than  an  hour)  and  appears  to  answer 
every  ordinary  requirement.  According  to  Parry  *  it  is  not  as 
accurate  for  high-grade  material  as  his  reduction  method,  des- 
cribed below  (10). 

i.  Author's  Modification  of  Pearce's  Method  (6). — In  a  thin 
spun-iron  crucible  of  about  60  cc.  capacity,  melt  about  8  grams 
of  sodium  hydroxide.  (I  take  about  3  inches  of  the  stick  hydrox- 
ide, broken  into  short  pieces.)  Heat  until  the  moisture  is  expelled 
and  quiet  fusion  attained.  After  cooling,  add  0.5  gram  of  the 
finely  ground  ore,  cover  the  crucible  with  a  loosely-fitting  porcelain 
cover,  and  heat,  at  first  very  cautiously  to  avoid  spattering,  and 
then  with  the  full  flame  of  a  Bunsen  burner  until  the  fusion  is 
quiescent.  Remove  the  cover  and  pour  the  melt  into  a  clean  metal- 
lic dish  floating  in  a  beaker  of  water.  I  use  a  2 -1-inch  nickel  dish. 
It  is  best  to  cover  the  hot  cake  with  a  small  porcelain  crucible 
cover,  dropping  within  the  dish,  to  prevent  mechanical  loss  in 
case  the  cake  cracks  and  flies  apart  violently.  Place  a  little  cold 
water  in  a  5|-inch  casserole  and  set  the  hot  crucible  therein; 
then  turn  the  latter  on  its  side  so  as  to  admit  the  water,  and 
heat  to  boiling.  Move  the  crucible  about  with  a  glass  rod, 


*  London  Mining  Journal,  Sept.  25,  1909.     See  also  Parry's  excellent  book, 
'The  Assay  of  Tin  and  Antimony." 

246 


TIN.  247 

and  when  the  outside  is  clean  wash  it  off  so  as  to  remove  the 
crucible  with  the  fingers.  The  inside  of  the  crucible  may  still 
contain  some  of  the  undissolved  melt.  Pour  in  a  little  water, 
acidify  with  hydrochloric  acid,  and  bring  the  dilute  acid,  by 
means  of  a  glass  rod,  in  contact  with  any  adhering  melt.  When 
all  is  dissolved,  wash  the  solution  into  the  casserole.  Now  add 
the  detached  cake  and  the  crucible-cover  with  the  top  (provided 
with  a  loop)  up.  Cover  the  casserole  and  add  about  30  cc.  of 
strong  hydrochloric  acid,  which  should  prove  an  ample  excess. 
Heat  to  boiling  and  the  cake  will  quickly  dissolve.  Now  remove 
and  wash  off  the  watch-glass  covering  the  casserole,  and,  by 
means  of  a  bent  iron  wire,  lift  out  the  crucible-cover  and 
wash  it! 

2.  Transfer  the  solution,  which  should  contain  no  residue  of 
undecomposed  ore  (although  there  may  be  some  scales  of  iron 
oxide  from  the  crucible)  to  a  tall  narrow  beaker,  or,  better,  a 
12  or  i6-oz.  conical  flask  with  a  wide  mouth.  The  flask  should 
be  marked  at  the  200  cc.  point.  Add  to  the  solution  50  cc.  of 
strong  hydrochloric  acid  and  then  dilute  with  hot  water  to  200 
cc.  Prepare  a  piece  of  sheet  nickel  by  rolling  a  strip  about  7 
inches  long  and  i  inch  wide  into  a  loose  coil.  This  may  be 
introduced  into  and  removed  from  the  flask  by  means  of  a  nickel 
wire  or  strip,  either  permanently  attached  to  the  coil  or  pro- 
vided with  a  hook  at  the  end.  Place  the  coil  in  the  flask,  cover 
the  latter  and  heat  the  liquid  to  boiling.  Maintain  in  gentle 
ebullition  for  20  minutes,  when  the  tin  in  solution  will  all  have 
been  reduced  to  the  stannous  condition.  Remove  from  the 
heat  and  at  once  add  a  small  piece  of  marble  (equivalent  to 
about  f-inch  cube)  so  as  to  fill  the  flask  with  carbon  dioxide, 
and  place  the  covered  flask  in  running  water  to  cool  as  rapidly 
as  possible.  When  the  liquid  is  at  room  temperature,  remove 
the  coil  of  nickel  (which  will  not  be  greatly  attacked),  rinsing  it 


248  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

off  with  a  mixture  of  i  part  of  strong  hydrochloric  acid  and  3 
parts  water,  so  as  not  to  reduce  the  acid  strength  of  the  solution. 
Now  add  a  little  starch  liquor  (xm,  2)  and  titrate  at  once  with 
standard  iodine  solution  to  a  permanent  blue  color.  The  car- 
bon dioxide  in  the  flask  is  usually  quite  sufficient  as  a  preven- 
tive of  oxidation,  but  it  is  well  to  agitate  the  mixture  as  little  as 
possible  during  the  titration  and  to  deliver  the  iodine  solution 
with  the  tip  of  the  burette  well  down  in  the  flask. 

None  of  the  ordinary  constituents  of  ores  interfere  with  this 
method.  Both  arsenic  and  antimony  in  the  ous  condition  in 
weak  acid  solution  consume  iodine,  but  in  a  solution  contain- 
ing at  least  one-fourth  of  its  volume  of  strong  hydrochloric  acid 
they  are  entirely  without  effect. 

3.  Instead  of  reducing  the  tin  solution  as  described  in  2,  the 
following  procedure  may  be  adopted  to  insure  accuracy:*  Trans- 
fer the  solution  from  the  casserole  to  a  flask  of  about  500  cc. 
capacity  and  marked  at  the  200  cc.  point.  Add  50  cc.  of  strong 
hydrochloric  acid  and  dilute  the  solution  with  hot  water  to  200 
cc.  Add  about  i  gram  of  finely  powdered  C.  P.  antimony  and 
boil  the  mixture  gently  for  fifteen  minutes,  shaking  occasionally. 
Now  discontinue  the  heat  and  connect  with  an  apparatus  capable 
of  giving  a  rapid  current  of  carbon  dioxide.  The  connection  is 
made  by  means  of  a  stopper  carrying  two  tubes.  The  first,  which 
is  connected  with  the  carbon  dioxide  apparatus,  dips  below  the 
surface  of  the  solution  in  the  flask,  and  the  second  or  outlet 
tube  simply  passes  through  the  stopper  and  has  the  outer  end 
bent  downward  so  as  to  dip  slightly  below  the  surface  of  some 
water  or  mercury.  This  allows  any  tendency  to  back  pressure 
to  be  instantly  detected.  While  passing  a  rapid  stream  of  gas, 


*  W.  H.  Low,  Jour.  Am.  Chem.  Soc.,  XXIX,  66;   also  Ibbotson  and  Brearly, 
Analyst,  1902,  25. 


TIN.  t    '  249 

again  heat  the  contents  of  the  flask  to  boiling  and  boil  for  two  or 
three  minutes.  Cool  quickly  by  surrounding  the  flask  with  cold 
water,  and  take  care  that  the  current  of  carbon  dioxide  is  strong 
enough  to  offset  the  back  pressure  due  to  sudden  condensation. 
When  cold,  loosen  the  stopper  somewhat  and  introduce  about 
5  cc.  of  starch  solution,  cork  quickly  and  take  to  the  burette. 
Introduce  the  spit  of  the  burette  well  into  the  flask  and  titrate 
with  the  standard  iodine  solution,  while  rotating  the  flask  gently 
and  avoiding  violent  agitation. 

4.  Ores   containing   pyrites   should   be   given   a   preliminary 
treatment  with  aqua  regia.     Filter  off  the  insoluble  residue  con- 
taining the  tin,  ignite  it  at  a  low  temperature  in  the  iron  crucible 
to  be  used  for  the  fusion,  and  then  proceed  with  assay  as  usual. 

In  giving  this  preliminary  treatment  to  material  containing 
tin  in  a  soluble  form,  it  is  of  course  necessary  to  evaporate  the 
aqua  regia  mixture  to  hard  dryness  and  take  up  again  in  dilute 
nitric  acid  before  filtering. 

5.  The  iodine  solution  may  be  prepared  by  dissolving  about 
ii  grams  of  iodine  in  a  little  water  with  the  addition  of  about  20 
grams  of  potassium  iodide,  and  diluting  to  i  liter.     On  the  basis 
of  0.5  gram  of  ore  taken  for  assay,  i  cc.  will  equal  about  one  per 
cent,  of  tin.     Standardize  as  follows:    Weigh  exactly  0.2  gram 
of  pure  powdered  arsenious  oxide,  place  in  a  6-oz.  flask  and 
dissolve  by  warming  with  a  little  dilute  sodium  hydroxide  solu- 
tion.    When  dissolved,  dilute  to  about   100  cc.  with  cold  water, 
add  a  few  drops  of  phenolphthalein  solution  as  indicator  and 
make  slightly  acid  with  hydrochloric  acid.     Now  cool  to  room 
temperature  or  cooler.     Finally  add  3-4  grams  of  sodium  acid 
carbonate   and    a   little   starch   liquor*   and  titrate   to   a  per- 
manent blue  color  with  the  iodine  solution.     Pay  no  attention 
t)  a  brownish  discoloration  toward   the  end,  but  proceed  slowly 

*  If  an  acid  starch  solution  is  used  add  it  before  neutralizing. 


250          TECHNICAL  METHODS  OF  ORE  ANALYSIS, 

until  a  single  drop  of  the  iodine  produces  a  strong  permanent 
blue  color.  0.2  gram  of  arsenious  oxide  =  0.2404  gram  of  tin, 
from  which  the  value  of  the  iodine  solution  may  be  calculated. 
The  solution  does  not  change  materially  during  a  week,  but  it  is 
not  safe  to  use  a  standard  that  is  older. 

6.  Method  of  E.  V.  Pearce  for  the  Determination  of  Tin  in 
Ores,  etc.  —  Fuse*  from  8  to  10  grams  of  stick  sodium 
hydroxide  in  a  2^-inch  nickel  dish  with  the  addition  of  a 
sprinkling  of  finely-powdered  charcoal,  keeping  the  dish  covered 
with  a  porcelain  crucible-cover.  When  the  sodium  hydroxide 
is  thoroughly  fused,  remove  the  lamp  and  allow  to  cool 
slightly. 

7.  Weigh  from  0.2  to  0.5  gram,  according  to  its  supposed 
richness,  of  the  finely  powdered  ore,  place  it  in  a  thin  layer  over 
the  cooled  melt  in  the  dish,  and  sprinkle  a  little  more  charcoal 
over  the  ore.  Cover  the  dish  and  heat  again,  cautiously  at  first 
to  avoid  spattering,  finally  with  the  full  power  of  a  Bunsen  burner 
for  5  or  10  minutes,  or  until  no  further  action  is  seen.  Allow  to 
cool,  and  when  cold  the  separation  of  the  cake  may  be  effected 
by  squeezing  ths  dish  in  the  hand.  Transfer  the  cake  to  an 
evaporating-dish  (a  glazed  iron  dish  is  ordinarily  employed),  add 
water,  and  thoroughly  clean  and  wash  the  nickel  dish  and  cover. 
Now  cover  the  evaporating-dish  and  add  sufficient  strong  hydro- 
chloric acid  to  effect  a  complete  solution  of  the  cake,  with  the 

*  For  this  description  I  am  indebted  to  Dr.  Richard  Pearce,  who  has  kindly 
written  it  with  the  consent  of  Mr.  E.  V.  Pearce,  his  nephew.  Dr.  Pearce  describes 
the  method  as  he  has  seen  it  in  daily  use  at  the  works  of  Messrs.  Williams,  Harvey 
&  Co.,  Ltd.,  in  Cornwall,  with  which  his  nephew  is  connected.  In  regard  to  its 
accuracy,  Dr.  Pearce  states:  "I  have  seen  the  method  tried  on  various  ores  and 
mixtures,  the  latter  being  prepared  with  percentages  of  tin  known  only  to  myself, 
and  am  quite  satisfied  with  its  accuracy  and  rapidity.  In  my  opinion  it  is  far 
ahead  of  any  method  which  has  yet  been  suggested  for  the  assay  of  tin,  especially 
in  low  grade  ores. " 


TIN.  251 

exception,  possibly,  of  some  gelatinous  silica*  Under  ordinary 
circumstances  the  latter  may  be  disregarded,  but,  if  desired,  it 
may  be  removed  by  filtering  through  glass  wool.  Transfer  the 
solution  to  a  tall  narrow  beaker,  add  a  few  rods  of  iron  (nail- 
rod),*  about  3  or  4  inches  long,  cover  the  beaker  and  warm  it 
gently  to  effect  a  free  evolution  of  hydrogen.  The  ferric  chloride 
is  reduced  to  a  ferrous  salt,  the  yellow  color  giving  place  to  a  pale 
green,  and  then  the  stannic  chloride  is  reduced  to  stannous  chlo- 
ride. The  whole  reduction  is  complete  in  30  minutes  or  even 
less.  Now  place  the  beaker  and  contents  in  a  dish  in  which  cold 
water  is  circulating  until  the  solution  is  as  cold  as  possible. 
Remove  and  wash  the  iron  rods,  add  a  little  starch  liquor,  and 
the  solution  is  then  ready  for  titration  with  a  standard  iodine 
solution. 

8.  The  latter  is  prepared  in  the  usual   way  by  dissolving 
iodine  in  a  solution  of  potassium  iodide,  and  is  standardized 
with  pure  tin  or  pure  arsenious  oxide.     About  a  N/io  strength 
is  convenient. 

9.  In  the  case  of  ores  containing  pyrites,  the  latter  should 
be  oxidized  before  the  fusion.     To  avoid  possible  loss  in  roast- 
ing, it  is  best  to  treat  with  aqua  regia  until  the  sulphides  are 
decomposed,  then  dilute,  filter,  and  ignite  the  residue,  contain- 
ing all  the  tin  oxide,  at  a  low  temperature  in  a  porcelain  capsule 
(it  being  unnecessary  to  burn  off  all  the  carbon)  and  proceed  with 
it  as  described  above. 

10.  In  regard  to  his  method,  Mr.  E.  V.  Pearce  writes:  "I 
should  explain  to  you  that  the  merit  of  my  process   lies  in  the 
ease  with  which  the  tin  is  obtained  in  solution.     The  titratiorf 
with  iodine  which  I  am  using  has  been  elaborated  by  L.  Parry 
and  is  described  in  detail  in  his  book,  "The  Assay  of  Tin  and 

*  Mr.  Pearce  now  uses  sheet  nickel  as  the  reducing  agent.     I  have  likewise 
found  nickel  preferable  to  iron. 


252  TECHNICAL    METHODS  OF  ORE  ANALYSIS. 

Antimony."     The   advantages   of   the   process,    in   conjunction 
with  the  iodine  titration,  over  any  other  known  tin  assay  are: 

"  i.    The  ease  with  which  all  the  tin  is  obtained  in  solution; 
"  2.    The  absence  of  any  nitrations; 
"  3.    No  separation  of  other  metals  is  necessary; 
"  4.    The   speed   with   which   an   assay   can   be   made,  —  i^ 
hours  being  sufficient  for  any  ores." 

NOTE.  —  Mr.  E.  V.  Pearce  has  recently  called  my  attention  to  the  fact  that  the 
omission  of  charcoal  in  the  decomposition,  according  to  my  modification  of  his 
method,  is  apparently  permitted  by  the  use  of  an  iron  crucible.  When  a  nickel 
crucible  is  used,  the  decomposition  is  frequently  incomplete  if  charcoal  is  omitted, 
but  iron  filings  appear  to  serve  equally  as  well  as  charcoal.  The  iron  of  the  cru- 
cible is  therefore  a  factor  in  the  reactions,  and  Mr.  Pearce  prefers  the  method  I 
describe,  as  being  more  convenient  than  the  use  of  either  charcoal  or  iron  filings. 

ii.  Parry's  Method  for  the  Assay  of  Tin  Ore.*— Tin  ores  may 
be  either  pyritic  or  non-pyritic.  Pyritic  ores  holding  more  than  two 
per  cent,  sulphur  must  be,  and  non-pyritic  ores  may  be,  treated 
with  nitric  acid  before  reduction,  as  tin  sulphide  is  volatile  at  a 
red  heat.  Weigh  5  grams  of  the  ore,  ground  as  finely  as  possible, 
either  directly  into  a  porcelain  boat,  or  treat  in  an  evaporating 
dish  with  a  watch-glass  cover  with  20  cc.  of  dilute  nitric  acid, 
and  carefully  evaporate  to  complete  dryness.  Digest  the  residue 
with  dilute  nitric  acid  and  filter.  Dry  the  washed  residue,  ignite 
it  in  the  dish,  and  then  transfer  it  to  a  porcelain  boat  and  heat 
it  to  low  redness  for  two  hours  in  a  slow  current  of  hydrogen  or 
coal  gas.  Coal  gas  is  much  more  convenient  to  use  and  quite 
as  effective  as  hydrogen.  The  boat  is  2^  by  £  inch,  and  two  at 
a  time  may  be  placed  in  a  porcelain  or  glass  tube  12  inches  long 
and  f  inch  bore,  which  is  then  placed  in  the  reduction  furnace. 
A  very  convenient  form  of  gas  reduction  furnace,  with  clay  body, 

*  L.  Parry,  London  Mining  Jour.,  Sept.  25,  1909;    also  Parry's  "The  Assay 
of  Tin  and  Antimony." 


TIN.  253 

brass  gas  jets,  and  asbestos  rings  to  fit  over  the  ends  of  the  tube 
against  the  clay  covers,  is  made  in  6-inch  lengths.  The  ends  of 
the  tube  should  project  about  3  inches  at  each  end  of  the  furnace, 
and  should  be  closed  with  rubber  stoppers  fitted  with  glass  tubes 
as  shown;  the  escaping  gas  (about  4  bubbles  per  second)  is 
passed  through  dilute  hydrochloric  acid,  in  which  any  volatilized 
tin  is  condensed.  In  ores  holding  not  more  than  2  per  cent, 
sulphur — that  is  to  say,  in  99  out  of  100  samples  of  black  tin  or 
tin  barilla,  as  bought,  treatment  with  nitric  acid  may  be  omitted. 
In  these  direct  reduction  assays  the  tube  is  washed  out,  after 
the  reduction  is  complete,  with  hydrochloric  acid  and  potassium 
chlorate,  also  the  glass  leading  tube.  The  solution  is  mixed 


FIG.  19. 

with  that  through  which  the  gas  bubbled,  reduced  with  iron 
and  titrated  for  tin  with  iodine.  This  generally  adds  o.i  or  0.2 
per  cent,  on  the  main  tin  assay.  Where  treatment  of  the  ore 
with  nitric  acid  is  adopted  as  a  method,  the  tube  may  still  be 
similarly  washed  out,  and,  together  with  the  gas  liquor,  tested 
for  tin,  as  a  check,  for  instance,  against  volatilization  of  tin  on 
account  of  sulphur  in  the  gas.  A  two-way  gas  branch  is  used; 
one  jet  supplies  gas  to  the  tube,  the  other  supplies  gas  for  heating 
the  furnace.  After  the  reduction  allow  the  boats  to  cool  in  the 
furnace,  and,  when  cold,  transfer  each  boat  and  its  contents  to 
a  400-cc.  beaker  and  treat  with  150  cc.  of  hydrochloric  acid  and 
5  cc.  of  nitric  acid.  Allow  the  assay  to  stand  in  a  warm  place 
until  the  action  abates,  then  boil  for  a  few  minutes,  dilute  with 
an  equal  bulk  of  water  and  filter.  Wash  the  residue  well  with 


254  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

hot  acid  water,  then  with  hot  water,  and  then  dry  and  ignite  it. 
Fuse  the  ignited  residue  with  4  or  5  parts  of  a  mixture  of  sodium 
carbonate  (free  from  chlorine)  and  borax,  in  a  platinum  crucible. 
Dissolve  the  melt  in  hydrochloric  acid  and  precipitate  with  zinc, 
as  usual.  The  residue  rarely  holds  more  than  0.5  per  cent,  of 
the  total  tin  in  the  ore.  Instead  of  fusing  the  residue  as  above, 
it  may  be  fused  with  about  2  inches  of  stick  sodium  hydroxide 
in  an  iron  crucible  over  a  Bunsen  burner.  Dissolve  the  melt  in 
hydrochloric  acid  and  precipitate  on  zinc  as  usual.  Make  up 
the  main  solution  to  500  cc.,  pipette  off  the  equivalent  of  i  gram 
into  an  8-oz.  flask,  reduce  with  iron  wire  and  filter.  Precipitate 
the  filtrate  with  strips  of  sheet  zinc  as  usual.  Dissolve  the  metallic 
sponge  in  hydrochloric  acid  and  titrate  at  the  boiling-point  with 
standard  ferric  chloride  solution. 

In  precipitating  the  tin  with  zinc,  neutralize  the  solution 
(which  should  be  freely  acid)  with  thin  strips  of  zinc.  Use  an 
excess  of  zinc  at  the  beginning,  as,  if  the  neutralization  is  effected 
too  slowly,  tin  is  apt  to  remain  unprecipitated.  When  the  action 
ceases  pour  a  little  of  the  liquor  into  a  beaker  containing  some 
hydrogen  sulphide  water;  if  the  precipitate  is  white  all  the  tin 
has  been  thrown  down.  Pour  away  tne  mother  liquor  as  closely 
as  possible,  after  allowing  any  floating  particles  of  metal  to  settle. 
The  best  plan  is  to  pour  the  liquid  from  the  flask  into  a  beaker, 
which  is  then  rapidly  filled  with  water  from  the  tap.  Press  the 
larger  pieces  of  spongy  tin  against  the  side  of  the  beaker  with  a 
glass  rod,  after  which  they  will  readily  settle.  The  addition  of 
a  drop  or  two  of  ammonia,  or  pouring  the  liquid  to  and  fro  from 
one  beaker  to  another,  will  generally  insure  the  settling  of  the 
lighter  particles.  Wash  the  metal  in  the  beaker  back  into  the 
flask  with  180-200  cc.  of  hydrochloric  acid,  to  dissolve  the  tin 
and  zinc,  and  bring  the  liquid  to  a  boil  as  rapidly  as  possible, 
with  the  addition  of  a  granule  of  zinc.  The  flask  should  be 


TIN.  255 

provided  with  a  rubber  stopper  through  which  passes  a  short 
length  of  glass  tubing.  If  the  acid  is  not  brought  to  a  boil  rapidly 
the  metal  may  be  completely  dissolved  while  there  is  still  air  in 
the  flask,  and  some  stannic  chloride  be  formed.  When  the  solu- 
tion is  complete,  and  the  liquid  boiling,  titrate  at  once  with  ferric 
chloride.  One  drop  of  the  ferric  chloride  solution  in  excess  should 
produce  a  plain  yellow  tinge.  The  end-point  is  more  marked 
the  hotter  and  more  acid  the  solution. 

Under  ordinary  circumstances  it  is  better  to  let  the  action 
cease  completely  when  precipitating  with  the  zinc,  but  in  the 
rare  cases  when  titanium  is  present  (as  evidenced  by  the  violet 
color  of  the  solution  during  the  precipitation),  the  liquor  must 
be  poured  off  from  the  tin  and  zinc  while  it  is  still  slightly  acid, 
the  titanium  being  then  all  in  solution  as  sesquichloride.  Also, 
the  sponge  of  tin  and  zinc  should  be  washed  once  with  water 
slightly  acidulated  with  hydrochloric  acid.  Under  these  circum- 
stances no  titanium  hydroxide  is  left  with  the  tin  and  zinc. 
Ti2Cl4  is  oxidized  by  ferric  chloride,  though  it  is  unaffected  by 
iodine.  In  the  case  of  an  insoluble  silicious  residue  from  solu- 
tion of  the  ore  after  gas  reduction,  which  is  apparently  poor  in 
tin  and  appears  to  be  rich  in  titanium,  it  would  be  a  convenient 
plan,  after  fusing  and  dissolving  in  hydrochloric  acid,  to  reduce 
the  solution  with  iron  and  titrate  with  iodine,  instead  of  precipi- 
tating with  zinc  for  the  ferric  chloride  assay,  as  the  silicic  acid 
sometimes  deposited  from  hydrochloric  acid  solutions  during 
zinc  precipitation  may  carry  down  titanic  acid  with  it  or  occlude 
titanous  chloride  mechanically.  If,  however,  any  titanium  got 
through  into  the  hydrochloric  acid  solution  for  ferric  chloride 
titration,  its  presence  would  at  once  be  shown  by  the  color. 
On  rich  material  the  ferric  chloride  titration  should  be  employed 
whenever  possible,  as  the  iodine  titration,  even  under  the  best 
conditions,  has  a  slight  tendency  to  give  low  results. 


256  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

12.  Preparation  and  Standardization  of  the  Ferric  Chloride 
Solution. — The  ferric  chloride  solution  should  be  made  up  2 
liters  at  a  time,  from  a  concentrated  stock  solution  made  by 
dissolving  piano  wire  in  hydrochloric  acid,  peroxidizing  with 
nitric  acid  and  evaporating  twice  with  hydrochloric  acid  to  dry- 
ness,  and  then  dissolving  in  hydrochloric  acid.  It  is  standardized 
against  i  gram  of  the  purest 'tin,  filed  wth  a  fine  file.  The  ferric 
chloride  solution  may  also  be  made  by  dissolving  180  grams  of 
the  yellow  commercial  lump  salt,  which  is  roughly  Fe2Cl6.i2H2O, 
in  about  200  cc.  of  hydrochloric  acid  and  evaporating  to  dryness. 
The  residue  is  dissolved  in  300  cc.  of  hydrochloric  acid  and  diluted 
to  2  liters.  The  evaporation  is  to  free  the  solution  from  nitric 
acid  and  arsenic.  Use  only  the  purest  and  strongest  hydro- 
chloric acid. 

To  standardize,  weigh  i  gram  of  pure  finely  divided  tin  into 
an  8-oz.  flask,  add  strong  hydrochloric  acid  until  the  flask  is  about 
three-fourths  full,  insert  a  rubber  stopper  provided  with  a  few 
inches  of  small  glass  tubing,  and  boil  the  mixture  until  solution 
is  complete.  Do  not  boil  too  rapidly,  as  this  weakens  the  hydro- 
chloric acid  too  much  before  the  tin  is  dissolved.  Neither  should 
the  liquid  come  to  a  boil  too  slowly,  as  the  tin  might  then  be  all 
dissolved  before  the  air  in  the  flask  was  thoroughly  expelled, 
and  stannic  chloride  be  formed.  When  solution  is  complete, 
titrate  the  boiling-hot  solution  at  once.  Use  a  fast-running 
burette  with  a  glass  stopcock.  Two  or  three  minutes  delay  in 
titrating  will  not  show  a  perceptible  effect,  but  after  five  minutes, 
oxidation  is  apparent  and  increases  rapidly.  The  end-point  of  the 
titration  is  indicated  by  a  yellow  tinge,  which  is  produced  by  an 
excess  of  i  drop  of  the  ferric  chloride  solution.  If  the  liquid  in 
the  flask  turns  dark  greenish  after  the  titration,  the  ferric  chloride 
is  contaminated  with  nitric .  acid,  i  cc.  should  equal  about  2 
per  cent,  of  tin,  on  the  basis  of  one  i  gram  taken  for  assay. 


TIN. 


257 


In  the  assays  the  main  portion  of  the  titration  must  be  done 
with  the  above  ferric  chloride  solution,  but  the  finish  may  be 
with  a  solution  of  half  or  quarter  strength,  in  order  to  obtain  a 
more  exact  ending. 

Notes. — Any  copper  in  the  tin  ore  is  found  in  the  nitric  acid 
solution,  though  traces  may  remain  with  the  SnC>2.  In  the  iron 
wire  stage,  the  arsenic  which  escaped  extraction  with  nitric  acid 
and  volatilization  in  the  reduction  tube,  is  partly  evolved  as  AsH3 
and  partly  precipitated  with  antimony  in  the  metallic  form. 
It  comes  down  as  a  brown  flocculent  deposit,  which  contains  3 
or  4  per  cent,  of  its  weight  in  tin.  As  there  is  generally  only 
i  or  2  per  cent,  at  most,  and  usually  under  0.5  per  cent.,  of 
arsenic  in  a  tin  ore,  the  loss  of  tin  from  this  cause  is  quite  neg- 
ligible, but  as  a  check  one  should  save  the  iron  wire  and  precipi- 
tates and  filter-papers,  and  examine  them  from  time  to  time  for 
tin.  It  will  be  found,  as  in  the  case  of  the  deposit  in  the  tube, 
and  the  dilute  hydrochloric  acid  through  which  the  escaping  gas 
bubbles,  that  only  the  merest  traces  of  tin  are  lost  in  these  oper- 
ations. Further,  the  hydrochloric  acid  solution  of  the  reduced 
metal  may  be  done  in  a  conical  flask  with  a  rubber  stopper  and  tube 
dipping  under  water,  to  assure  oneself  that  there  is  no  appreciable 
loss  by  volatilization  of  SnCl2. 

If  the  ore  contains  wolfram  it  is  mostly  found  as  WOs  in 
the  residue  from  the  hydrochloric  acid  and  nitric  acid  extraction 
of  the  reduced  metal,  from  which  it  may  be  removed,  before 
fusion,  with  ammonia.  Any  tungsten  which  gets  into  the  main 
solution  comes  down  as  blue  oxide  with  the  iron  wire  pre- 
cipitate, and  any  which  is  fused  with  sodium  carbonate  and 
borax  should  be  removed  by  reducing  the  hydrochloric  acid 
extract  of  the  melt  with  iron  wire  before  precipitating  with 
zinc.  In  general,  all  the  antimony  and  some  of  the  lead 
in  the  ore  will  be  found  in  the  main  hydrochloric  acid  solu- 


258  TECHNICAL    METHODS    OF    ORE    ANALYSIS. 

tion,  while    some   of    the    lead   will    be  obtained  in  the  nitric 
acid  extract. 

After  the  nitric  acid  evaporation  the  residue  may  be  boiled 
with  hydrochloric  acid  (about  50  cc.),  diluted  and  filtered,  though 
in  this  case  the  extract  must  be  tried  for  tin  as  a  matter  of  pre- 
caution. It  will,  in  general,  hold  all  the  copper  and  most  of  the 
arsenic,  antimony,  lead  and  iron,  though  one  can  never  be  sure 
that  the  residue  is  free  from  the  oxides  of  these  metals.  Occa- 
sionally this  hydrochloric  acid  extract  will  hold  a  little  tin.  The 
residue  is  reduced  in  the  usual  manner. 

Except  with  impure  ores  the  reduction  with  iron  wire  may 
be  omitted,  as  it  is  always  an  advantage  to  save  a  filtration  when 
possible,  and  as  the  small  amount  of  antimony  usually  present 
is  evolved  as  stibine  during  the  zinc  precipitation.  In  this  case 
the  aliquot  part  of  the  solution  is  at  once  precipitated  with  zinc. 
The  boiling  hydrochloric  acid  solution  for  titration  with  ferric 
chloride  must,  however,  be  free  from  black  powder  of  Cu,  Sb, 
etc.,  and  from  tungsten  blue  in  suspension  or  solution.  (Lower 
oxides  of  tungsten  in  solution  give  a  brownish  pink  or  light  claret 
colored  solution.)  During  precipitation  with  zinc  the  solution 
should  be  freely  acid  to  start  with,  and  in  the  presence  of  Ti  or 
Mo  should  be  distinctly  acid  when  poured  off,  as  titanium  and 
molybdenum  interfere  with  the  ferric  chloride  titration,  titanium 
sesquichloride  reducing  ferric  chloride. 

When  copper,  or  appreciable  amounts  of  antimony,  or  arsenic, 
or  bismuth  are  present,  reduction  from  iron  must  precede  zinc 
precipitation.  Instead  of  doing  this  with  iron  wire  in  a  flask 
use  a  400-cc.  beaker  (tall  shape),  and  one  strip  of  sheet-iron 
about  '4-in.  in  width,  and  of  sufficient  length  to  leave  about  i 
inch  above  the  surface  of  the  liquid.  This  will  be  easy  to  wash. 
The  assay  must  be  filtered  hot,  and  the  paper  thoroughly  but 
rapidly  washed  with  hot  water  strongly  acid  with  hydrochloric 


TIN.  259 

acid.  Under  the  assay  conditions  the  residue  is  free  from  tin. 
After  zinc  precipitation  care  must  be  taken  to  insure  that  no 
floating  particles  of  metal  are  poured  off  with  the  mother  liquor, 
or  left  in  the  beaker  after  redissolving  in  hydrochloric  acid.  The 
mother  liquor  must  always  be  tested  with  hydrogen  sulphide.  The 
assay  for  titration  is  brought  to  a  boil  as  rapidly  as  possible,  and 
should  begin  to  boil  before  the  metal  is  all  in  solution.  The 
addition  of  a  granule  of  zinc  effects  this.  The  zinc  used  in  pre- 
cipitation must  be  good  thin  sheet-zinc,  free  from  tin. 


CHAPTER  XXVII. 

TITANIUM. 

i.  Method  for  Iron  Ores.* — Treat  5  grams  of  the  ore  with 
30  cc.  of  strong  hydrochloric  acid.  Heat  gently  until  as  com- 
plete a  decomposition  as  possible  is  effected  and  then  evaporate 
to  dryness.  Take  up  the  residue  in  20  cc.  of  strong  hydrochloric 
acid,  dilute  sufficiently  and  filter  off  the  insoluble  residue.  The 
titanium  will  be  found  in  both  the  residue  and  nitrate;  they  are, 
therefore,  treated  separately  as  follows: 

Residue. — Dry  and  ignite  the  residue  in  a  platinum  crucible 
so  as  to  burn  off  all  the  carbon  of  the  filter.  Cool,  moisten  with 
water,  add  5  to  10  drops  of  strong  sulphuric  acid  and  enough 
hydrofluoric  acid  to  dissolve  the  silica,  and  heat  cautiously  until 
fumes  of  sulphuric  acid  are  given  off.  Reserve  the  crucible  and 
contents  for  treatment  described  later. 

Filtrate. — Heat  to  boiling  in  a  large  beaker.  Remove  from 
the  heat  and  add  gradually  a  mixture  of  10  cc.  of  a  strong  solution 
of  ammonium  acid  sulphite  (see  foot-note,  p.  130)  and  20  cc.  of  am- 
monia, stirring  constantly.  A  precipitate  forms  at  first  which  redis- 
solves.  If  the  precipitate  fails  to  redissolve  by  vigorous  stirring, 
at  any  time  during  the  addition  of  the  sulphite,  add  a  few  drops 
of  hydrochloric  acid  to  clear  the  liquid  and  then  continue  with 


*  Adapted  from  Blair.     Chem.  Anal,  of  Iron. 

260 


TITANIUM.  26i 

the  sulphite.  When  all  but  2  or  3  cc.  of  the  sulphite  solution 
has  been  added  replace  the  beaker  over  the  lamp.  The  solu- 
tion should  smell  quite  strongly  of  sulphur  dioxide.  Now  add 
ammonia  water,  drop  by  drop,  until  the  solution  is  quite  decol- 
orized, and  finally  a  slight  greenish  precipitate  is  formed  which 
remains  even  after  vigorous  stirring.  When  this  occurs  add 
the  remaining  2  or  3  cc.  of  the  sulphite  solution.  This  should 
produce  a  white  precipitate  which  usually  redissolves,  leaving  a 
clear  and  almost  decolorized  solution.  Should,  however,  any 
precipitate  remain  undissolved,  add  hydrochloric  acid,  drop  by 
drop,  until  the  solution  is  clear.  It  should  smell  perceptibly 
of  sulphur  dioxide.  If  the  reagents  are  used  in  exactly  the  pro- 
portions indicated,  the  reactions  will  take  place  as  described 
and  the  operations  will  be  readily  and  quickly  carried  out.  If 
the  ammonium  acid  sulphite  solution  is  weaker  than  it  should 
be,  of  course  all  the  ferric  chloride  may  not  be  reduced  and  the 
solution  at  the  end  of  the  operation  described  above  may  not  be 
decolorized  or  smell  of  sulphur  dioxide.  In  that  case  add^more 
of  the  ammonium  acid  sulphite  solution,  without  ammonia,  until 
the  solution  smells  strongly  of  sulphur  dioxide,  and  then  add 
ammonia  until  the  slight  permanent  precipitate  appears,  and 
redissolve  it  in  as  few  drops  of  hydrochloric  acid  as  possible.  The 
solution  being  now  nearly  neutral,  the  iron  in  a  ferrous  condition 
and  an  excess  of  sulphur  dioxide  being  present,  add  5  cc.  of 
strong  hydrochloric  acid  to  make  it  decidedly  acid  and  insure 
complete  decomposition  of  any  excess  of  ammonium  acid  sulphite 
which  may  be  present.  Boil  the  solution  while  passing  a  stream 
of  carbon  dioxide  through  it  until  every  trace  of  sulphur  dioxide 
is  expelled.  Now  add  a  few  drops  of  bromine  water  and  cool 
the  solution  by  placing  the  beaker  in  cold  water.  To  the  cold 
solution  add  ammonia  water  from  a  small  beaker  very  slowly, 
finally  drop  by  drop,  with  constant  stirring.  The  green  ferrous 


262  TECHNICAL  METHODS   OF   ORE  ANALYSIS. 

hydroxide  which  forms  at  first  dissolves  on  stirring  to  a  perfectly 
clear  solution,  but  subsequently,  although  the  green  precipitate 
dissolves,  a  whitish  one  remains  and  the  next  drop  of  ammonia 
increases  the  whitish  precipitate  or  gives  it  a  reddish  tint.  Finally 
the  greenish  precipitate  remains  undissolved,  even  after  vigorous 
stirring,  and  another  drop  of  ammonia  makes  the  whole  precipi- 
tate appear  green.  If,  before  this  occurs,  the  precipitate  does 
not  appear  decidedly  red  in  color,  dissolve  the  green  precipitate 
by  a  drop  or  two  of  hydrochloric  acid,  add  i  or  2  cc.  of  bromine 
water,  then  ammonia  as  before.  Repeat  this  until  the  reddish 
precipitate  is  obtained,  followed  by  the  green  coloration  as 
described  above.  Dissolve  this  green  precipitate  in  a  very  few 
drops  of  acetic  acid  (sp.  gr.  1.04),  when  the  precipitate  remaining 
will  be  quite  red  in  color.  Now  add  i  cc.  of  acetic  acid  and 
dilute  the  solution  with  boiling  water  so  that  the  beaker  may 
be  about  four-fifths  full.  Heat  to  boiling,  boil  i  minute,  lower 
the  flame  and  filter  as  rapidly  as  possible  through  a  5j-inch 
filter.  Wash  once  with  hot  water.  The  filtrate  should  run 
through  clear,  but  in  a  few  minutes  it  will  appear  cloudy  owing 
to  the  precipitation  of  ferric  hydroxide  formed  by  the  action  of 
the  air.  The  points  to  be  observed  are  the  red  color  of  the 
precipitate  and  the  clearness  of  the  solution  when  it  first  runs 
through. 

Dry  the  filter  and  precipitate  in  the  funnel.  Clean  out  any 
precipitate  still  adhering  to  the  beaker  by  wiping  it  with  filter- 
paper  and  dry  this  paper.  Transfer  the  thoroughly  dried  pre- 
cipitate to  a  small  porcelain  mortar,  removing  it  from  the  filter- 
paper  as  completely  as  possible.  Roll  up  the  filter  and  other 
bits  of  paper  used  and  burn  them  on  the  lid  of  the  crucible  in 
which  the  original  residue  was  treated  and  transfer  the  ash  to 
the  mortar.  Grind  the  precipitate  and  ash  with  3  to  5  grams 
of  sodium  carbonate  and  a  little  sodium  nitrate  and  transfer 


TITANIUM.  2  S3 

it  to  the  crucible  containing  the  residue  which  was  treated  with 
hydrofluoric  and  sulphuric  acids.  Clean  the  mortar  and  pestle 
by  grinding  a  little  more  sodium  carbonate  and  add  this  to  the 
rest  in  the  crucible.  Fuse  the  whole  for  half  an  hour  or  more, 
cool,  dissolve  the  fused  mass  in  hot  water  and  filter  from  the 
insoluble  ferric  oxide,  etc.  This  residue  contains  all  the  titanium 
in  the  form  of  sodium  titanate.  (The  filtrate  contains  all  the 
phosphorus  in  the  ore  as  sodium  phosphate.)  Dry  the  residue, 
transfer  it  to  the  crucible  in  which  the  last  fusion  was  made, 
burn  the  filter  and  add  the  ash,  and  then  fuse  the  whole  with 
5  grams  of  dry  sodium  carbonate.  Allow  the  crucible  to  cool 
and  then  pour  strong  sulphuric  acid  into  it  very  gradually.  When 
the  effervescence  slackens,  warm  the  crucible  slightly  and  con- 
tinue the  gradual  additions  of  sulphuric  acid  and  the  careful 
applications  of  increased  heat  until  the  mass  becomes  liquid 
and  the  ferric  oxide  is  all  dissolved.  Now  heat  very  carefully 
until  copious  fumes  of  sulphuric  anhydride  are  given  off,  then 
allow  the  crucible  to  cool  and  pour  the  contents,  which  should 
be  just  fluid  when  cold,  into  a  beaker  containing  about  250  cc. 
of  cold  water.  Add  to  it  about  50  cc.  of  a  strong  aqueous  solution 
of  sulphur  dioxide,  or  2  or  3  cc.  of  a  strong  solution  of  ammonium 
acid  sulphite.  Filter  if  necessary,  nearly  neutralize  with  ammonia, 
allow  to  stand  until  entirely  decolorized  and  then  add  a  filtered 
solution  of  20  grams  of  sodium  acetate  in  one-sixth  the  volume 
of  the  solution  of  acetic  acid  of  1.04  sp.  gr.  and  heat  to  boiling.. 
The  titanic  acid  will  be  precipitated  almost  immediately  in  a 
flocculent  condition,  nearly  or  quite  free  from  iron.  Boil  for  a 
few  minutes,  allow  the  titantic  acid  to  settle,  filter,  wash  with. 
hot  water  containing  a  little  acetic  acid,  dry,  ignite,  and  weigh  as. 
TiO2.  Multiply  this  weight  by  0.6005  to  obtain  that  of  the 
titanium. 

If  the  TiO2,  after  ignition,  appears  discolored,  owing  to  the 


264  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

presence  of  a  little  ferric  oxide,  fuse  it  with  a  little  sodium 
carbonate,  add  sulphuric  acid  to  the  cold  fused  mass,  dis- 
solve, and  repeat  the  precipitation  with  sodium  acetate  in 
the  presence  of  sulphur  dioxide  and  acetic  acid,  precisely  as 
before. 

2.  Method    for   Pig  Iron,   etc. — Treat   5   grams  of  drillings 
in  a  covered  beaker  with  80  cc.  of  nitric  acid  of  1.2  sp.  gr.    When 
violent  action  has  ceased  add  10  cc.  of  strong  hydrochloric  acid. 
Remove  the  cover  and  evaporate  to  dryness.     Replace  the  cover 
and  heat  until  the  ferric  nitrate  is  about  all  decomposed.     Cool, 
add  about  30  cc.  of  hydrochloric  acid,  heat  gently  until  the  iron 
oxide  is  dissolved  and  evaporate  to  dryness  again,  best  in  an 
air-bath.     Cool,  dissolve  in  30  cc.  of  dilute  hydrochloric  acid, 
and  then  filter  and  wash  with  hot  water. 

Treat  the  residue  and  filtrate  separately,  precisely  as  described 
above  for  ores  (i). 

3.  Colorimetric   Method  for    Iron    Ores.*  —  Take  o.i  gram 
of  the  finely  powdered  mineral  and  mix  it  in  a  platinum  crucible 
with  0.2  gram  of  sodium  fluoride,  also  finely  powdered.     Add 
3  grams  of  sodium  pyrosulphate  without  mixing.     Fuse  care- 
fully, holding  the  burner  in  the  hand.     Heat  gently  till  the  effer- 
vescence ceases  and  copious  fumes  of  sulphuric  acid  are  evolved. 
This  takes  only  2  or  3  minutes.     When  cold,  dissolve  the  mass 
in  the  crucible  in  1 5  to  20  cc.  of  cold  water  and  filter  the  solution. 
The  filtrate  and  washings  need  not  exceed  30  cc.     If  a  residue 
remains,  it  can  be  treated  again  by  the  same  method,  after  burning 
the  filter,  but  the  amount  of  titanium  found  by  a  second  fusion 
is  usually  very  small. 

To  the  solution  add  i  cc.  of  hydrogen  peroxide  and  a  few 
cubic  centimeters  of  dilute  sulphuric  acid  and  compare  the  color 

*  Method  of  W.  A.  Noyes,  Jour,  of  Anal,  and  Appl.  Chem.,  V,  39. 


TITANIUM.  265 

(orange- red  to  yellow)  with  that  of  solutions  containing  known 
amounts  of  titanium.  Nessler  tubes  may  be  used  for  this  pur- 
pose, and  the  solutions  are  all  brought  to  the  same  volume,  say 
30  or  50  cc.  For  a  standard  solution,  dissolve  titanic  oxide  in 
hot  concentrated  sulphuric  acid  and  dilute  the  solution  till  i  cc. 
contains  i  mg.  of  TiC>2.  In  diluting  it  is  best  to  use  dilute  sul- 
phuric acid  at  first,  to  prevent  the  precipitation  of  titanic 
oxide.* 

The  colors  produced  are  more  or  less  affected  by  the  presence 
of  iron,  and  it  is  therefore  advisable  to  add  to  the  comparison- 
tubes  an  amount  of  ferric  sulphate  corresponding  approximately 
to  that  in  the  solution  which  is  being  tested.  A  solution  of  ferric 
ammonium  alum  answers  well  for  this  purpose,  and  all  that  is 
necessary  is  to  match  the  color  of  the  solution  of  the  mineral 
before  adding  hydrogen  peroxide  to  it.  If  this  is  done,  titanium 
can  be  readily  determined  in  the  presence  of  very  considerable 
amounts  of  iron.  Thus,  0.02  mg.  of  titanic  oxide  can  be  detected 
in  30  cc.  of  water  in  the  presence  of  o.i  gram  of  ferric  oxide  in 
the  form  of  sulphate.  This  would  correspond  to  0.02  per  cent, 
for  o.i  gram  of  mineral. 

Determinations  based  on  a  comparison  of  tints  are  especially 
valuable  for  the  estimation  of  small  quantities  of  elements,  and 
for  most  cases  where  titanium  requires  determination  the  above 
method  is  amply  accurate.  It  works  excellently  with  magnetite 
and  other  iron  ores.  There  appears  to  be  no  appreciable  error 
caused  by  the  volatilization  of  titanium  as  fluoride. 

4.  A  qualitative  test  for  titanium  can  be  made  in  5  minutes 
as  follows:  Mix  a  little  of  the  powdered  ore  with  sodium  fluoride, 
add  sodium  pyrosulphate,  and  fuse  as  above.  Cool  by  dipping 
the  crucible  in  cold  water.  Add  2  or  3  cc.  of  dilute  sulphuric 

*  See  5. 


265  TECHNICAL   METHODS    OF   ORE  ANALYSIS. 

acid  and  10  cc.  of  water.  Dissolve  by  boiling.  Divide  the 
solution  in  two  portions,  and  to  one  add  a  few  drops  of  hydrogen 
peroxide.  A  comparison  with  the  solution  to  which  no  hydrogen 
peroxide  has  been  added  will  show  at  once  whether  titanium  is 
present  or  not. 

5.  Preparation  of  Standard  Solution  of  Titanic  Oxide. — I  have 
found  difficulty  in  preparing  a  standard  solution  of  titanium  by 
dissolving  titanic  oxide  in  hot  concentrated  sulphuric  acid.  The 
following  method  is  satisfactory  : 

Ignite  pure  titanic  acid  until  all  water  of  hydration  is  ex- 
pelled. Weigh  0.5  gram  into  a  6-oz.  flask,  add  10  cc.  of  strong 
sulphuric  acid  and  5  grams  of  potassium  sulphate.  Heat  over 
a  free  flame  until  the  titanic  acid  is  dissolved  and  the  solu- 
tion is  clear.  Cool,  dilute  with  125  cc.  of  1:4  sulphuric  acid, 
transfer  to  a  5oo-cc.  measuring  flask,  and  make  up  to  the  mark 
with  cold  water.  When  perfectly  cool,  again  adjust  to  the  mark 
and  mix  thoroughly,  i  cc.  will  contain  i  mg.  of  TiO2.  A 
more  accurate  method  of  preparing  this  standard  solution  may 
be  found  in  Bulletin  No.  305  of  the  U.  S.  Geological  Survey,  p.  in. 


CHAPTER  XXVIII. 

TUNGSTEN. 

THE  following  method  for  the  determination  of  tungsten  in 
wolframite  and  oxidized  ores  is  modified  from  one  devised  by 
O.  P.  Fritchle. 

i.  Hydrofluoric  Acid  Method. — Treat  0.5  gram  of  the  very 
finely  powdered  ore  in  a  small  platinum  dish  with  equal  parts 
of  strong  hydrochloric  and  hydrofluoric  acids.  Digest  on  a 
water-bath  until  solution  is  complete,  adding  more  of  each  acid 
from  time  to  time  if  necessary.  It  may  require  from  one  to 
several  hours  to  effect  complete  decomposition  of  the  ore. 
Usually  a  perfect  solution  may  be  obtained.  Any  tin  oxide 
present  will  be  unaffected.  Finally,  evaporate  to  about  15  cc. 
with  an  excess  of  hydrochloric  acid.  A  yellow  precipitate  of 
H2WO4  may  separate  during  the  final  evaporation,  owing  to 
the  expulsion  of  the  hydrofluoric  acid  that  holds  it  in  solution. 
This  will  do  no  harm  provided  it  can  all  be  removed  from  the 
dish.*  Transfer  the  solution  and  any  precipitate  to  a  6-oz.  flask, 
add  20  cc.  of  strong  hydrochloric  acid  and  8  cc.  of  strong  nitric  acid. 
Boil  down  to  about  10  cc.  This  will  expel  any  remaining  hydro- 
fluoric acid  and  precipitate  the  tungsten  as  tungstic  acid,  H2WO4. 
Dilute  with  50  cc.  of  hot  water  and  allow  to  simmer  at  a  gentle 
heat  for  about  half  an  hour,  or  until  the  tungstic  acid  has  settled 
clear.  Filter,  wash  well  with  hot  water  slightly  acidulated  with 

*  Warming  with  a  few  drops  of  ammonia  will  usually  dissolve  any  adherent 

residue  easily. 

267 


268  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

hydrochloric  acid,  and  then  dissolve  the  tungstic  acid  on  the 
filter  by  pouring  warm  dilute  ammonia  over  it,  using  as  little 
as  possible,  and  washing  the  filter  with  the  same  solution.  Receive 
the  filtrate  in  a  weighed  platinum  dish.  Evaporate  the  solution 
on  a  water-bath  to  dryness,  and  then  ignite  the  residue  at  a  red 
heat,  cool  and  weigh  as  WO  3.  The  cold  residue  should  be  of 
a  bright  canary-yellow  color.  Multiply  the  weight  of  the  WO  3 
by  0.793  to  obtain  the  weight  of  the  tungsten,  from  which  the 
percentage  in  the  ore  may  be  calculated. 

2.  Fusion   Method   for   Wolframite. — Fuse  0.5   gram  of  the 
very  finely  ground  ore  with   2-3    grams   of   sodium  potassium 
carbonate  in  a  platinum  crucible  for    from  one-half    to  three- 
quarters  of  an  hour.     Dissolve  the  fused  mass  in  boiling  water. 
The  tungsten  goes  into  solution  as  sodium  or  potassium  tungstate, 
together  with  alkali  silicate  and  also  stannate,  if  tin  be  present. 
The  residue  contains  the  iron,  manganese,  calcium,  and  magne- 
sium.    Filter  and  wash  with  hot  water.     Rinse  the  residue  into 
a   beaker  and   warm  with   dilute   hydrochloric   acid.     If  gritty 
particles   remain  undissolved  filter  them  off  through   the  filter 
last  used  and  wash  with  hot  water.     Dry  and  ignite  the  residue 
and  again  fuse  it  with  the  mixed  carbonates.     Dissolve  the  fused 
mass  as  before,  filter  and  unite  the  filtrate  with  the  first  filtrate. 

3.  Having  thus  obtained  an  aqueous  solution  of  alkali  tung- 
state, add  to  it  an  excess  of  nitric  acid  and  evaporate  to  dry- 
ness  on  a  water-bath.     Again  add  a  little  nitric  acid  and  evap- 
orate to  dryness  a  second  and   third   time.     Finally  heat  the 
residue  in  a  drying-oven  at  120°  C.  for  some  time,  then  moisten 
with  strong  nitric  acid  and  allow  to  stand  for  15  or  20  minutes. 
Now  add  a  hot  5  per  cent,  solution  of  ammonium  nitrate  and 
filter  the  mixture,  washing  well  with  ammonium  nitrate  solution 
slightly  acidified  with  nitric  acid  to  remove  all  the  sodium  and 
potassium  salts.     Finally,  wash  once  or  twice  more  with  a  hot, 


TUNGSTEN.  269 

very  dilute  ammonium  nitrate  solution  and  then  dry  the  filter 
and  contents  and  transfer  the  latter  as  completely  as  possible  to 
a  weighed  platinum  crucible.  Moisten  the  paper  with  a  strong 
solution  of  ammonium  nitrate,  dry  it  and  incinerate  over  the 
crucible  in  a  coil  of  platinum  wire.  Ignite  the  whole,  now,  with 
free  access  of  air.  If  the  tungstic  acid  is  not  pure  yellow  when 
cool,  moisten  with  a  few  drops  of  nitric  acid  and  repeat  the  ignition. 

4.  The  ignited  tungstic  acid  may  contain  silica  and  stannic 
oxide.    The  former  may  be  removed  by  warming  with  a  few  cubic 
centimeters  of  hydrofluoric  acid,  evaporating  to  dryness  and  ig- 
niting.   The  residue  consists  of  pure  tungstic  acid,  or  tungstic  acid 
and  stannic  oxide.     The  amount  of  the  latter  is  usually  so  small 
as  to  be  negligible.     If  desired,  however,  the  tin  may  be  vola- 
tilized as  stannic  chloride  by  ignition  with  ammonium  chloride. 
The  stannic  chloride  is  decomposed  by  the  moisture  of  the  air 
and  stannic  oxide  may  be  deposited  on  the  outside  of  the  crucible. 
To  prevent  this,  place  the  crucible  in  a  larger  one  and  keep  the 
outer  crucible   covered   until  the   ammonium   chloride   is   com- 
pletely expelled.     Now  heat  the  inner  crucible  with  free  access  of 
air  until  its  contents  become  of  a  pure  yellow  color.     Cool  and 
weigh.     Repeat1  the  ignition  with  six  or  eight  times  as  much 
ammonium  chloride  as  there  is  precipitate  until  the  weight  of 
the  residual  WO3  becomes  constant.     The  tungstic  acid  becomes 
dark  on  igniting  in  the  absence  of  air  and  only  assumes  its  true 
color  and  weight  on  igniting  with  free  access  of  air. 

The  weight  of  the  WO3  multiplied  by  0.793  gives  that  of 
the  tungsten. 

5.  Another  method  of  precipitating  the  tungstic  acid  from 
the  solution  of  alkali  tungstate  is  that  of  Berzelius,  as  follows: 
Neutralize  the  greater  part  of  the  alkali  with  nitric  acid,  being 
very  careful,  however,  to  still  leave  the  solution  slightly  alkaline. 
The  amount  of  nitric  acid  to  use  is  best  ascertained  by  a  blank 


270  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

test  on  the  same  amount  of  alkali  carbonates  as  was  taken  for 
the  fusion.  Now  add  a  solution  of  mercurous  nitrate  until  it 
produces  no  further  precipitation.  If,  on  slowly  adding  the 
mercurous  nitrate,  the  precipitate  seems  to  be  getting  unduly 
large,  indicating  too  great  alkalinity,  add  nitric  acid  drop  by 
drop  until  an  added  drop  of  mercurous  nitrate  produces  no 
cloud.  Heat  to  boiling,  allow  the  precipitate  to  settle,  then 
filter  and  wash  with  water  containing  mercurous  nitrate.  Dry 
the  filter  and  contents  and  then  ignite  in  a  platinum  crucible 
under  a  hood.  Weigh  as  WO  3. 

The  tungstic  acid  thus  obtained  almost  always  contains 
silica  and  possibly  stannic  oxide.  It  may  be  purified  as  described 
above  (4). 

6.  The  Determination  of  Tungstic  Acid  in  Low-Grade  Ores.* — 
Weigh  5  grams  or  more  of  the  sample.  Digest  in  a  4-inch  porcelain 
dish  with  20  cc.  of  a  25  per  cent,  solution  of  sodium  hydroxide 
(free  from  chloride)  for  30  to  45  minutes  on  a  water-bath.  Now 
dilute  the  mixture  somewhat,  add  a  little  sodium  peroxide  to 
oxidize  any  decomposition  products  of  sulphides,  transfer  to  a 
250-cc.  measuring-flask  and  make  up  to  the  mark.  After  mixing, 
filter  through  a  dry  filter,  reject  a  little  of  the  first  filtrate  that 
runs  through,  and  collect  200  cc.  of  the  remainder  in  a  measuring- 
flask.  Transfer  this  portion  to  a  beaker,  acidify  with  nitric  acid 
and  then  make  alkaline  with  ammonia.  Heat  to  boiling,  filter 
and  wash.  Acidify  the  filtrate  slightly  with  dilute  nitri:  acid, 
add  mercurous  nitrate  solution  (prepared  as  below)  in  excess, 
and  then  a  few  drops  of  dilute  ammonia.  On  warming  and 
stirring,  the  precipitate  settles  readily.  Filter,  wash  the  precipi- 
tate with  weak  mercurous  nitrate  solution,  and  then  ignite  the 
precipitate  and  paper  together  in  a  weighed  porcelain  crucible. 

*  H.  W.  Hutchin  and  F.  J.  Tonks,  Inst.  Min.  and  Met.  Bull.,  No.  56. 


TUNGSTEN.  271 

A  platinum  crucible  may  be  used  if  the  ore  is  free  from  arsenic. 
Weigh  as  WO3. 

For  assays  of  ores  and  tailings,  the  sample  may  be  reduced 
to  a  sufficient  degree  of  fineness  in  a  wedgewood  mortar,  but 
for  concentrates  an  agate  mortar  is  necessary;  fine  powdering 
is  essential.  For  decomposing  charges  containing  not  more  than 
0.4  gram  of  tungstic  acid,  20  cc.  of  a  25  per  cent,  solution  of 
sodium  hydroxide  will  suffice.  The  decomposition  is  rapid;  0.4 
gram  of  wolfram  concentrates  being  decomposed  in  15  minutes 
to  the  extent  of  98  per  cent,  of  the  tungsten  content.  As  a  rule, 
however,  it  is  best  to  take  from  30  to  45  minutes  for  the  decom- 
position. 

The  mercurous  nitrate  solution  may  be  conveniently  prepared 
from  mercury.  Digest  from  2  to  3  ozs.  in  a  large  beaker  or 
flask  for  ij  hours  with  25  cc.  of  nitric  acid  (sp.  gr.  1.4)  and  75 
cc.  of  water,  on  a  hot  plate  which  will  keep  the  liquid  nearly 
at  the  boiling-point.  Allow  to  stand,  hot,  over  night.  Dilute 
to  about  400  cc.,  which  will  give  a  saturated  solution  with  a 
minimum  of  free  acid. 

The  weighed  WO3  may  be  tested  for  silica,  if  desired,  by 
treatment  in  platinum  with  hydrofluoric  acid.  The  loss  is  usually 
very  slight. 

In  the  presence  of  scheelite  the  method  is  not  applicable, 
since  this  mineral  is  only  partially  attacked,  under  the  conditions 
of  the  assay. 

7.  Method  by  Fusion  with  Alkalies. — Treat  5  grams  of  the 
finely  powdered  ore  with  hydrofluoric  acid  in  a  platinum  dish, 
finally  evaporating  to  dryness.  Wash  the  dried  residue  into  a 
beaker  with  water,  to  a  volume  of  about  40  cc.  Add  5  cc.  of 
nitric  acid  and  warm  gently  to  remove  the  bulk  of  any  mispickel 
present  and  then  dilute  considerably  and  allow  to  stand  over 
night.  Filter  the  mixture  and  wash,  dry,  and  ignite  the  residue. 


272  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Again  powder  the  residue  in  an  agate  mortar,  transfer  it  to  a 
nickel  dish  and  fuse  it  with  a  mixture  of  sodium  peroxide  and 
hydroxide.  Extract  the  melt,  when  cold,  with  water  and  dilute 
to  250  cc.  in  a  measuring-flask.  Mix  well  and  filter  through  a 
dry  filter,  rejecting  the  first  portion.  Measure  200  cc.  of  the 
filtrate  (representing  4  grams  of  ore)  to  be  used  for  the  actual 
assay.  Transfer  to  a  beaker,  acidify  with  nitric  acid,  then  make 
plainly  alkaline  with  ammonia,  boil,  filter,  and  wash.  Add  nitric 
acid  to  the  filtrate  until  it  is  neutral  or  faintly  acid,  then  add 
mercurous  nitrate  solution  (described  in  6)  in  excess,  and  finally 
a  little  freshly  precipitated  mercuric  oxide,  or  a  few  drops  of 
dilute  ammonia.  Warm  and  stir  the  mixture  until  it  settles  well 
and  then  filter,  washing  the  precipitate  with  weak  mercurous  nitrate 
solution.  Ignite  paper  and  precipitate  in  a  platinum  crucible  and 
weigh  the  residue  as  WO3.  The  WO3  should  be  tested  for  silica 
by  treatment  with  hydrofluoric  acid. 


CHAPTER    XXIX. 
URANIUM   AND   VANADIUM. 

1.  Method  for  Uranium. — Treat  i  gm.  of  the  ore  (or  more  if 
very  low  grade)  in  an  8-oz.  flask  with  10  cc.  of  strong  hydro- 
chloric acid  and  5  cc.  of  strong  nitric  acid.     Allow  to  simmer 
gently  over  a  low  heat  until  solution  is  as  complete  as  possible, 
and  then  boil  to  dryness.     This  may  be  done  by  manipulating 
the  flask  in  a  holder  over  a  free  flame.     Add  3  cc.  of  hydrochloric 
acid  and  5  cc.  of  water  to  the  residue,  warm  for  a  short  time, 
occasionally  agitating,  then  dilute  with  25  cc.  of  hot  water  and 
filter,  washing  with  warm  water.     Receive  the  filtrate  in  a  small 
beaker. 

2.  Pass  hydrogen  sulphide  into  the  liquid  to  separate  copper, 
lead  and  other  metals  of  this  group,  filter,  wash  with  hydrogen 
sulphide  water  and  boil  the  filtrate  to  expel  the  hydrogen  sul- 
phide.    Concentrate  to  100  cc.  if  necessary,  oxidize  with  hydrogen 
peroxide  (usually  10  cc.),  'and  then  neutralize  with  dry  sodium 
carbonate,  adding  2  or  3  grams  in  excess.     Boil  the  liquid  for 
about  15  minutes,  or  until  the  yellowish  uranium  precipitate  dis- 
solves, leaving  a  brown  precipitate  which  is  largely  iron.     Filter 
and  wash  the  iron  precipitate  once  or  twice  with  hot  water,  and 
reserve  the  filtrate.     Dissolve  the  iron  precipitate  in  the  least 
possible  amount  of  nitric  acid  (i  :  i),  dilute  somewhat  if  nee. 
essary,  add  10  cc.  of  hydrogen  peroxide  and  repeat  the  precipi- 
tation with  sodium  carbonate  precisely  as  before.     Filter  into  the 
beaker  containing  the  first  filtrate.     Wash  well  with  hot  water. 

273 


274  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

3.  Evaporate  the  united  filtrates  from  the  iron  precipitation 
to  a  volume  of  about  200  cc.,  add  10  cc.  of  strong  nitric  acid  and 
boil  until  all  CC>2  is  expelled.     Neutralize  the  free  acid  with 
ammonia   (until  a  slight  pernament  precipitate  appears),  then 
add  4  cc.  of  nitric  acid  for  each  100  cc.  of  liquid.     Now  add  10 
cc.  of  a  20  per  cent,  lead  acetate  solution,  and  enough  of  a  strong 
solution  of  ammonium  acetate  to  neutralize  the  nitric  acid  present 
and  substitute  acetic  acid  for  it.     The  object  is  to  precipitate  the 
vanadium    as  lead  vanadate  in  an  acetic  acid  solution.     The 
ammonium  acetate  solution  may  be !  made  by  mixing  80  cc.  of 
strong  ammonia,  100  cc.  of  water,  and  70  cc.  of  acetic  acid  99 
per  cent.  pure. 

4.  Heat  the  liquid  containing  the  lead  vanadate  precipitate 
on  the  steam-bath  for  one  hour  or  more,  filter  on  a  tight  filter 
and  wash  with  warm  water.     Dissolve  the  precipitate  in  the  least 
possible  quantity  of  hot  dilute  nitric  acid,  neutralize  as  before, 
add  3  cc.  of  nitric  acid  in  excess,  then  2  cc.  of  lead  acetate  solu- 
tion and  repeat  the  precipitation  of  lead  vanadate  by  adding 
ammonium  acetate  in  excess.     Filter  and  add  the  filtrate  to  the 
one   from  the  first  precipitation  of  lead  vanadate.     Evaporate 
the  united  filtrates  from  the  lead  vanadate  to  about  400  c.c    Add 
10  cc.  of  strong  sulphuric  acid  to  separate  the  bulk  of  the  lead 
(derived  from  the  excess  of  lead  acetate)  as  PbSO4,  and  filter, 
washing  the  precipitate  with  cold  water.     Neutralize  the  filtrate 
from  the  PbSO4  with  ammonia  and  add  freshly  prepared  (NH4)HS 
until  the  solution  is  yellow  and  the  uranium  and  what  little  lead 
is  present  are  precipitated  as  sulphides.    Warm  up  mixture  gently 
until  the  sulphides  settle  well.     Filter  and  wash  slightly  with  warm 
water. 

5.  Dissolve  the  precipitate  in  a  No.  2  beaker  with  hot  dilute 
(i :  2)  nitric  acid,  add  5  cc.  of  strong  sulphuric  acid  and  evaporate 
until  the  latter  is  fuming.     Cool,  take  up  with  water,  boil,  let 


URANIUM  AND    VANADIUM.  275 

the   small   precipitate  of  PbSC>4  settle   until  the  liquid  is  cold, 
and   then   filter  it  off,  washing  with  very  dilute  sulphuric  acid 

(1:20). 

6.  Separation   of  Alumina:     Nearly  neutralizes    the    filtrate 
with  ammonia.     Have  the  solution  cold  (not  wanner  than  30°  C), 
and   add   powdered   ammonium   carbonate   in   about    2   grams 
excess.    This  will  precipitate  the  aluminum  and  hold  the  ura- 
nium in  solution.     Let  the  precipitate  settle,  filter,  and  wash  it 
with  warm  water.     If  the  precipitate  is  bulky,  or  is  at  all  yellow, 
dissolve  it  in  a  little  dilute  sulphuric  acid  and  reprecipitate  with 
ammonium  carbonate  as  before. 

7.  Acidify  the  filtrate,  or  combined  filtrates,  from  the  alumina 
with  sulphuric  acid  and  boil  to  thoroughly  expel  CO2.     Make 
the  liquid  slightly  alkaline  with  ammonia  while  it  is  hot,  and 
heat  gently  until  the   ammonium  uranate   collects  and  settles. 
Filter  and  wash  with  a  very-  dilute    solution    (2    per  cent.)  of 
ammonium  nitrate.     Do  not  allow  the  precipitate  to  run  dry 
on  the  filter  after  the  first  washing.     Dry  the  precipitate,  ignite 
it  in  a  porcelain  crucible   and  weigh   as  U3O8.     Dissolve  the 
ignited  residue  in  a  little  nitric  acid  and  test  it  with  H2O2  for 
vanadium.     Only  a  faint  brownish  tint  should  appear,  at  most. 
Rinse    the   solution    into    a   small   beaker   and   test  for  alum- 
ina    with     ammonium     carbonate.      Should     an.    appreciable 
amount  be  found    it  may  be  filtered  off,  ignited,  weighed  and 
deducted. 

8.  Volumetric  Method  for  Uranium. — Treat  i  gram  of  the 
ore  (or  more  if  very  low  grade)  in  an  8-oz.  flask  with  10  cc.  of 
strong  hydrochloric  acid  and  5  cc.  of  strong  nitric  acid.     Allow 
to  simmer  gently  over  a  low  heat  until  solution  is  as  complete 
as  possible,  and  then  boil  to  dryness.     This  may  be  done  by 
manipulating  the  flask  in  a  holder  over  a  free  flame.     Add  3  cc. 
of  hydrochloric  acid  and  5  cc.  of  water  to  the  residue  and  warm 


276  TECHNICAL  METHODS   OF  ORE  ANALYSIS. 

gently  until  solution  is  as  complete  as  before.  Now  add  25  cc. 
water  and  pass  in  hydrogen  sulphide  to  precipitate  the  mem- 
bers of  that  group.  Filter,  washing  with  hydrogen  sulphide 
water  at  least  7  times,  receiving  the  nitrate  in  a  fairly  large 
beaker.  Placing  a  boiling-rod  (p.  8)  in  the  liquid,  cover  the 
beaker  and  boil  off  the  hydrogen  sulphide.  Remove  from  the 
heat  and  add  10  cc.  of  H2O2.  Now  add  dry  sodium  carbonate 
in  small  portions  until  the  free  acid  is  neutralized  and  then  about 
2  grams  in  excess.  Boil  the  mixture  until  all  CO2  is  expelled 
and  the  precipitate,  on  standing,  settles  well.  At  this  point 
add  about  2  cc.  more  H2O2.  Filter,  washing  once  or  twice  with 
hot  water,  and  reserve  the  nitrate,  which  may  be  allowed  to  boil 
and  concentrate  while  waiting  for  the  next  step.  Rinse  the  bulk 
of  the  precipitate  from  the  filter  back  into  the  beaker,  then 
place  the  latter  under  the  funnel  and  dissolve  what  precipitate 
remains  on  the  filter  with  dilute  (i  :  i)  nitric  acid,  using  as  little 
as  possible.  Now  wash  the  filter  well  with  hot  water,  allowing 
all  to  run  into  the  beaker  containing  the  precipitate.  Warm 
the  mixture  until  the  precipitate  dissolves,  adding  more  acid 
if  necessary,  then  add  H2O2  and  precipitate  with  sodium  car- 
bonate precisely  as  before.  Filter  and  wash  the  precipitate  well 
with  hot  water.  Add  the  filtrate  to  the  first  one,  which  has 
been  concentrating,  and  boil  the  whole  to  a  bulk  of  about 
100  cc.  Now  remove  from  the  heat  (simply  to  prevent  froth- 
ing over)  and  cautiously  add  10  cc.  of  strong  nitric  acid,  and 
then  boil  again  until  all  the  CO2  is  expelled.  The  solution 
must  be  clear  and  boiling  hot  for  the  next  step. 

9.  Separation  of  Vanadium. — Place  in  a  large  beaker  about 
15  grams  of  ammonium  acetate,  5  grams  of  microcosmic  salt, 
50  to  75  cc.  of  water,  5  cc.  of  glacial  acetic  acid.  Place  a  boiling- 
rod  in  the  mixture  and  heat  to  rapid  boiling.  Have  arranged 
over  the  beaker  a  funnel  with  the  lower  end  drawn  out  so  as 


URANIUM   AND    VANADIUM.  277 

to  deliver  only  a  fine  stream.  Pour  the  hot  uranium  solution 
through  this  into  the  boiling  phosphate  solution.  Allow  to  boil 
a  few  minutes  after  all  has  run  through.  Now  remove  the  beaker 
from  the  heat,  cover  it  and  allow  to  stand  until  the  precipitate 
has  settled  well  and  then  filter.  Time  will  be  saved  by  pouring 
as  much  as  possible  of  the  clear  liquid  through  the  filter  before 
disturbing  the  precipitate.  Wash  the  precipitate  only  once, 
using  hot  water.  Now  rinse  it  back  into  the  beaker,  place  the 
latter  under  the  funnel  and  dissolve  what  remains  on  the  filter 
with  a  little  hot,  dilute  nitric  acid.  6  cc.  of  i  :  i  acid  are 
usually  sufficient.  Wash  the  filter  well  with  hot  water,  receiving 
all  in  the  beaker  containing  the  precipitate.  Warm  the  mixture 
until  the  precipitate  dissolves  and  dilute  to  about  75  cc ,  if 
necessary.  Heat  to  boiling  and  repeat  the  phosphate  precipi- 
tation precisely  as  before.  The  two  operations  will  remove 
practically  all  the  vanadium  and  leave  the  uranium  and 
aluminum  as  phosphates.  Filter  as  before  and  wash  four 
or  five  times  with  hot  water  containing  a  little  ammonium 
sulphate.  This  is  tedious  if  there  is  much  aluminum 
present.  Time  is  saved  by  stirring  the  precipitate  in  the 
apex  of  the  filter  with  the  jet  each  time.  Use  the  same  filter 
as  before. 

10.  Make  a  mixture,  in  a  small  beaker,  of  5  cc.  of  strong 
sulphuric  acid  and  15  cc.  of  water,  and  heat  nearly  to  boiling. 
Place  an  8-oz.  flask  under  the  funnel  and  pour  the  hot  acid 
mixture  slowly  over  the  precipitate  on  the  filter.  With  care, 
it  may  thus  be  all  dissolved,  although  the  hot  acid  may  be 
poured  through  again  if  necessary.  Wash  the  filter  well  with 
hot  water,  but  do  not  unduly  increase  the  volume  of  liquid  in 
the  flask.  This  should  not  be  allowed  to  much  exceed  50  to 
75  cc.  Heat  nearly  to  boiling  and  run  in  permanganate  to  a 
permanent  deep  pink  color,  to  oxidize  any  organic  matter 


278  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

present.  Now  add  10  grams  of  2o-mesh  C.  P.  zinc  and  allow 
to  stand  until  the  action  has  become  very  slow,  then  add  25  cc. 
more  water  and  10  cc.  more  sulphuric  acid.  When  the  zinc  has 
nearly  all  dissolved,  filter  the  solution  through  a  fresh  filter, 
washing  the  latter  and  residue  well  with  cold  water.  Receive 
the  filtrate  in  a  i6-oz.  flask.  Dilute  with  cold  water,  if  neces- 
sary, until  the  flask  is  about  half  full. 

11.  Cool  the  solution  to  room  temperature  and  titrate  with 
the  ordinary  permanganate  solution  used  for  iron  (p'.  119)  until 
a  single  drop  produces  a  pink  color  that  lasts  several  seconds. 
The  end-point  is  very  sharp,  although  the  color  may  soon  fade, 
owing,  possibly  to  traces  of  vanadium.     Note  the  burette-reading 
and  deduct  the  correction  required,  for  the  iron  in  the  10  grams 
of  zinc  used,  this  having  been  determined  by  a  blank  test.     As 
a  rule,  no  further  correction  is  required,  as  any  trace  of  vanadium 
present  appears  to  be  acted  on  so  slowly  in  the  cold  as  not  to 
seriously  interfere  with  obtaining  a  sharp  end-point.     As  a  pre- 
caution,   however,    add    i    gram    of   sodium  sulphite  and  boil 
the   solution    in    the   flask    until    all    smell  of   SO2   has  gone, 
and   then  7  or    8    minutes    more.     Add    cold  water  to  restore 
the    original    volume,    cool    to    room    temperature    and    titrate 
as  before.     Run  the  above    zinc  blank   in    the    same  way  and 
find  the  correction  required    for   the    combined   iron    and    im- 
purities   in   the   sulphite.     After    deducting  this  from  the  last 
reading,  the  remainder,  if  any,  may  be  credited    to  vanadium 
and    deducted    as    a    further    correction    from    the    uranium 
reading. 

12.  55.85  Fe=  140.583  U3O8,  or  i  Fe  =  2.5i7  U3O8.    If  the 
percentage  value  of  i  cc.  of  the  -permanganate  for  iron,  based  on 
0.5  gram  of  ore  taken,  is  given,  this,  multiplied  by  1.2585,  will 
give  the  percentage  value  of  i  cc.  for  U3O8,  when  i  gram  of 
uranium  ore  is  taken. 


URANIUM   AND   VANADIUM.  279 

13.  Method  for  Vanadium.* — Treat  i  gram  of  the  finely  divided 
ore  in  a  platinum  dish  with  about  3  cc.  of  strong  sulphuric  acid 
and  20  cc.  of  hydrofluoric  acid.  Evaporate  to  fumes  of  sulphuric 
acid  and  then  expel  the  latter  by  heating  over  a  naked  flame. 
Now  add  about  2  grams  of  sodium  carbonate  and  fuse.  Extract 
the  melt  with  hot  water  and  filter,  washing  with  hot  water.  Acidify 
the  filtrate  with  sulphuric  acid,  heat  nearly  to  boiling  and  pass 
in  hydrogen  sulphide  gas.  Arsenic  and  molybdenum  are  pre- 
cipitated, if  present,  and  V2O5  is  reduced  to  V2O4.  Filter,  washing 
with  hydrogen  sulphide  water.  Boil  the  filtrate  until  the  hydro- 
gen sulphide  is  completely  expelled  and  then  titrate  the  hot  solu- 
tion with  a  standard  solution  of  potassium  permanganate  to  the 
usual  pink  tinge  (XV,  8).  Then  again  reduce  by  passing  in 
sulphur  dioxide  gas,  boil  off  the  excess  and  repeat  the  titration. 
The  latter  result  is  apt  to  be  a  little  lower  than  the  former,  and  is 
to  be  taken  as  the  correct  one.  The  iron  factor  of  the  perman- 
ganate multiplied  by  0.916  will  give  the  vanadium  factor;  care 
being  taken  to  use  the  absolute  iron  factor  and  not  the  percentage 
factor  based  on  0.5  gram  of  ore  being  taken  for  analysis.  Uranium 
does  not  interfere  with  this  method,  which  I  regard  as  the  best 
of  the  many  technical  methods  proposed. 

14.  The  direct  use  of  a  solution  of  sulphur  dioxide,  or  an 
alkali  sulphite  for  reducing  the  vanadium  is  inadmissible  unless 
these  have  been  freshly  prepared,  or  a  blank  is  run,  since  they  are 
liable  to  contain  other  oxidizable  substances  than  SO2  or  a  sul- 
phite.    The  SO2  is  best  obtained  as  wanted  by  heating  a  flask 
containing  a  solution  of  SO2,  or  a  sulphite  to  which  sulphuric 
acid  has  been  added. 

15.  In  case  the  volume  of  permanganate  used  is  so  small  as  to 
make  doubtful  the  presence  of  vanadium,  it  is  necessary  to  apply 

*  Adapted  from  Hillebrand  and  Ransome,  Am.  Jour.  Sci.,  x,  also  Hillebrand, 
Bulletin  176,  U.  S.  Geological  Survey. 


280  TECHNICAL   METHODS    OF   ORE  ANALYSIS. 

a  qualitative  test,  which  is  best  made  as  follows:  The  solution 
is  evaporated  and  heated  to  expel  the  excess  of  sulphuric  acid, 
the  residue  is  taken  up  with  2  or  3  cc.  of  water  and  a  few  drops 
of  dilute  nitric  acid,  and  a  couple  of  drops  of  H2O2  are  added. 
A  characteristic  brownish  tint  indicates  vanadium.  Unless  the 
greater  part  of  the  free  sulphuric  acid  has  been  removed  the  appear- 
ance of  the  color  is  sometimes  not  immediate  and  pronounced, 
hence  the  above  precaution.  It  is  also  necessary  that  the  nitric 
acid  shall  be  in  considerable  excess,  since  in  neutral  or  only  faintly 
acid  solution  the  color  does  not  appear  strongly. 

For  determining  very  small  amounts  of  vanadium  in  rock 
analysis,  the  titrated  liquid  should  be  from  25  to  100  cc.  in  bulk 
and  the  permanganate  solution  very  dilute,  i  cc.  =  about  o.ooi 
gram  V2O5.  The  temperature  for  titration  should  be  from 
7o°-8o°  C.  ' 

16.  Volumetric  Method  for    Carnotite.* — This  mineral  con- 
tains uranium  and  vanadium  as  potassium  uranyl  vanadate. 

Dissolve  a  sample  of  the  ore  that  does  not  contain  more  than 
0.25  gram  of  U3O8  in  sulphuric  acid  (i :  5)  and  evaporate  to  fumes 
of  the  acid.  Cool,  dilute,  add  an  excess  of  sodium  carbonate  and 
boil  until  the  precipitate  settles  well.  Filter  and  wash  with  hot 
water.  Dissolve  the  precipitate  in  the  smallest  possible  amount 
of  sulphuric  acid  (1:5),  dilute,  add  an  excess  of  sodium  carbonate, 
boil,  filter  and  wash.  Acidify  the  combined  filtrates  and  wash- 
waters  with  sulphuric  acid.  Add  ammonium  phosphate  (0.5 
gram  is  usually  sufficient),  heat  to  boiling  and  make  alkaline  with 
ammonia;  boil  for  a  few  minutes,  filter  and  wash  with  hot  water 
containing  a  little  ammonium  sulphate,  which  prevents  the  finely 
divided  particles  of  the  precipitate  from  passing  through  the  filter. 

17.  The  filtrate  now  contains  the  vanadium  and  the  precipitate 

*  A.  N.  Finn,  Jour.  Am.  Chem.  Soc.,  xxvm,  1443. 


URANIUM   AND   VANADIUM.  281 

the  uranium.  Acidify  the  filtrate  with  sulphuric  acid,  pass 
sulphur  dioxide  into  it  until  it  becomes  blue,  boil  to  expel  the 
excess  of  sulphur  dioxide  and  titrate  while  hot  with  standard 
potassium  permanganate  solution.  The  iron  factor  of  the  per- 
manganate multiplied  by  1.631  gives  the  X^Os  factor,  or,  by 
0.9159,  the  vanadium  factor. 

18.  Dissolve  the  ammonium  uranyl  phosphate  in  dilute  sul- 
phuric acid,  add  some  granulated  zinc  and  let  the  action  con- 
tinue vigorously  for  at  least  thirty  minutes.  Remove  the  undis- 
solved  zinc  by  filtering  through  asbestos,  using  a  suction  pump. 
(These  are  Finn's  directions;  I  would  suggest  a  plug  of  absor- 
bent-cotton placed  in  the  neck  of  a  funnel,  without  a  suction 
pump,  instead  of  the  asbestos.)  Titrate  the  filtrate  at  about  60° 
C.  with  permanganate  (twentieth-normal).* 

The  iron  factor  of  the  permanganate  solution  multiplied  by 
2.5167  gives  the  UsOg  factor,  or,  by  2.133,  tne  uranium  factor. 

19.  Method  for  Vanadium. f  —  For  Products  Low  in  Silica: 
Weigh  out  from  0.250  to  i  gram  of  the  finely  powdered  material 
and  mix  in  a  nickel  crucible  of  about  25-0:.  capacity  with  3 
grams  of  sodium  peroxide;  cover  with  about  i  gram  more  of  the 
peroxide  and  heat  over  a  Bunsen  burner  for  three  or  four  minutes. 
It  is  not  necessary  to  heat  to  fusion;  a  dull  red  being  sufficient. 
When  the  darkening  which  gradually  takes  place  on  the  surface 
is  complete,  the  operation  may  be  considered  finished. 

Half  fill  a  500-cc.  beaker  with  cold  water  and  transfer  the 
cold  crucible  containing  the  melt  to  it.  Care  should  be  taken 
at  this  point,  as  the  reaction  between  the  peroxide  and  water  is 
violent.  It  is  well  to  float  the  crucible  in  the  beaker,  cover  the 
latter  with  a  large  watch  glass,  and  add  water  to  the  contents 

*  I  would  advise  making  a  blank  test  and  deducting  the  permanganate  re- 
quired. 

f  H.  F.  Watts,  Western  Chem.  and  Met.,  V,  408. 


282  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

of  the  crucible,  a  few  drops  at  a  time,  from  a  wash-bottle.  When 
solution  is  complete,  remove  and  wash  the  crucible,  heat  the  solu- 
tion to  boiling  and  pass  a  current  of  carbon  dioxide  through  it 
until  saturated.  Remove  from  the  heat,  allow  to  settle  and  filter. 
Wash  3  times  by  decantation,  and  3  times  on  the  filter,  using 
hot  water  containing  a  little  sodium  carbonate.  A  platinum  cone 
and  suction  may  be  employed  if  desired. 

Make  the  filtrate  just  acid  with  nitric  acid  and  boil  the  solu- 
tion a  few  moments.  Remove  the  beaker  from  the  heat  and 
add  to  the  hot  liquid  10  cc.  of  a  saturated  solution  of  lead  .ace- 
tate. If  the  excess  of  nitric  acid  is  not  too  great,  a  precipitate 
of  lead  vanadate  will  form  at  once.  However,  it  is  necessary 
to  also  add  a  few  grams  of  sodium  acetate  to  insure  the  complete 
neutralization  of  the  nitric  acid  and  the  absence  of  any  free  acid 
except  acetic.  The  lead  vanadate  is  insoluble  in  dilute  acetic 
acid,  but  dissolves  readily  in  nitric  acid.  Digest  the  mixture 
at  a  gentle  heat,  or  on  the  water-bath,  for  a  short  time,  until 
the  precipitate  settles  well,  and  then  filter  and  wash  with  hot 
water  containing  a  little  acetic  acid.  Rinse  the  bulk  of  the 
precipitate  (unless  very  small  in  amount)  into  an  8-oz.  flask, 
place  the  latter  under  the  funnel  and  pour  through  the  filter 
sufficient  dilute  nitric  acid  to  dissolve  any  remaining  precipitate, 
and  also  to  dissolve  that  in  the  flask,  but  avoid  using  more  acid 
than  required,  or  otherwise  unnecessarily  increasing  the  amount 
of  liquid  to  be  subsequently  evaporated.  Add  to  the  solution 
10  cc.  of  strong  sulphuric  acid  and  boil  to  fumes.  Cool,  dilute 
sufficiently  with  cold  water  and  filter  off  the  lead  sulphate, 
washing  with  cold  water.  Receive  the  filtrate  in  an  8-oz.  flask. 
Boil  the  filtrate  and  reduce  the  vanadium  (from  V2Os  to  VT2O4) 
by  adding  i  gram  of  sodium  sulphite  in  successive  small  portions. 
Boil  off  the  excess  of  sulphur,  dioxide,  testing  for  its  complete 
removal  as  follows:  Fit  a  stopper  and  delivery  tube  to  the  flask 


URANIUM  AND  VANADIUM.  283 

and  consider  the  operation  ended  when  the  escaping  steam  no 
longer  decolorizes  a  dilute  solution  of  potassium  permanganate, 
held  in  a  small  beaker.  Now  titrate  the  hot  solution  with  stand- 
ard potassium  permanganate  to  the  usual  pink  tinge,  employ- 
ing the  same  permanganate  as  is  used  for  iron  titrations.  The 
iron  value  of  the  permanganate  multiplied  by  1.632  will  give  the 
V2O 5  value,  or  by  0.916  the  vanadium  value. 

If  the  material  contains  arsenic  it  will  be  necessary  to  remove 
it.  A  convenient  point  at  which  to  do  this  is  after  the  reduction 
with  sodium  sulphite  and  expulsion  of  the  excess  of  sulphur 
dioxide.  Pass  hydrogen  sulphide,  filter,  washing  with  hydrogen 
sulphide  water,  boil  off  the  excess  of  hydrogen  sulphide  and 
titrate  as  before. 

The  burette  reading  should  be  corrected  as  follows:  To  150 
cc.  of  water  in  a  flask,  add  10  cc.  of  strong  sulphuric  acid  and 
i  gram  of  sodium  sulphite.  Boil  off  the  sulphur  dioxide  and 
titrate.  The  amount  of  permanganate  required  to  color  the 
solution  should  be  deducted  from  that  used  in  the  assay.  The 
correction  usually  amounts  to  0.2  cc. 

Method  for  Ores:  Treat  i  gram  of  the  finely  ground  ore  (or 
less  if  high  grade)  with  10  cc.  of  aqua  regia  and  evaporate  to 
dryness.  Add  10  cc.  of  nitric  acid  (1.20  sp.  gr.),  and  digest  on 
the  hot-plate  for  a  few  minutes.  Filter  off  the  silica,  etc.  Nearly 
neutralize  the  filtrate  with  sodium  hydroxide  and  then  pour  it 
with  constant  stirring  into  a  hot  solution  of  sodium  hydroxide 
contained  in  a  large  beaker.  A  stick  of  sodium  hydroxide  dis- 
solved in  200  cc.  of  water  is  about  the  right  strength.  Heat 
the  solution  to  boiling  and  pass  a  current  of  carbon  dioxide  to 
saturation.  Continue  from  this  point  as  described  above. 

Method  for  Products  Containing  much  Silica,  and  not  Readily 
Decomposed  by  Acids:  The  sodium  peroxide  method  may  be 
used,  but  in  this  case  it  will  be  necessary  to  remove  the  silica. 


2830  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

After  the  filtrate  from  the  iron  has  been  made  slightly  acid  with 
nitric  acid,  again  make  alkaline  with  ammonia,  and  add  3  or  4 
grams  of  ammonium  carbonate.  Place  the  beaker  on  a  warm 
plate  and  allow  to  stand  for  an  hour  with  occasional  stirring. 
Filter  off  the  voluminous  precipitate  of  silica,  using  a  i2-cm. 
filter  supported  on  a  platinum  cone,  and  employing  suction. 
This  precipitate,  though  somewhat  inclined  to  be  sticky,,  is  not 
difficult  to  filter  if  suction  is  used.  Wash  thoroughly  with  hot 
water  containing  a  little  ammonium  carbonate,  at  least  10  or  12 
times,  churning  up  the  precipitate  well  with  the  stream  from  the 
wash-bottle.  The  filtrate  is  now  freed  from  the  greater  part  of 
the  silica.  Again  make  it  slighly  acid  with  nitric  acid  and  pre- 
cipitate with  lead  acetate  as  before. 

When  using  the  acid  method  of  decomposition,  it  is  not 
always  safe  to  assume  that  the  vanadium  is  all  extracted  by 
treatment  of  the  ore,  crushed  to  8o-mesh  or  coarser,  with  dilute 
nitric  acid,  as  is  sometimes  recommended.  Some  vanadiferous 
sandstones  yield  to  this  treatment,  but  not  all.  To  make  sure 
of  complete  extraction,  the  ore  should  be  finely  ground  in  an 
agate  mortar  and  decomposed  first  with  aqua  regia. 

The  direct  reduction  and  titration  of  the  vanadium  in  the 
presence  of  the  accumulated  salts  of  the  analysis  is  inaccurate, 
the  end-point  being  uncertain,  and  successive  reductions  gen- 
erally failing  to  check.  It  is  therefore  always  necessary  to  sepa- 
rate the  vanadium  from  these  impurities  with  lead  acetate,  the 
titration  of  pure  vanadium  solutions  being  exact.  If  rapid  approx- 
imate results  are  wanted,  the  filtrate  from  the  iron  residue  may  be 
acidified  with  sulphuric  acid,  and  the  solution  reduced  and  titrated. 

The  method  as  described  has  the  advantage  over  the  ammonium 
carbonate  method  in  that  the  separation  of  the  iron  and  vanadium 
is  performed,  in  nearly  every  case,  in  a  single  operation,  and 
the  necessity  for  redissolving  and  reprecipitating  the  iron  residue 


URANIUM  AND  VANADIUM.  2&J 

is  obviated.  A  clean  separation  can  be  made  on  iron  vanadate, 
using  300  mg.  of  substance. 

The  carbon  dioxide  is  used  to  prevent  bumping  (it  also 
neutralizes  the  caustic  alkali,  which  would  otherwise  destroy 
the  filter. — A.  H.  L.),  although  in  some  cases  its  use  appar- 
ently gives  cleaner  separations,  due  possibly  to  the  tendency 
of  the  alkaline  carbonates  formed  to  hold  vanadium  in  solu- 
tion. 

20.  Note  by  the  Author. — I  would  suggest  the  following  pro- 
cedure for  removing  the  troublesome  silica.  It  appears  to  be 
generally  applicable : 

Treat  the  ore  as  described  in  Method  for  Ores  above  until  the 
silica  has  been  filtered  off.  Reserve  the  filtrate.  Ignite  the 
insoluble  residue  in  a  platinum  dish.  After  cooling,  treat  with 
sufficient  strong  hydrofluoric  acid  and  evaporate  on  the  water- 
bath  to  dryness.  Take  up  in  a  little  dilute  nitric  acid  and  again 
evaporate  to  dryness,  and  then  once  more  dissolve  in  a  little 
dilute  nitric  acid.  Filter,  if  necessary,  adding  the  filtrate  to  the 
one  reserved.  Ignite  the  residue  in  platinum,  and  then  transfer  ii 
to  an  iron  or  nickel  crucible  and  fuse  with  a  little  sodium  peroxide. 
Dissolve  the  melt  in  water,  add  the  reserved  filtrate,  and  then 
sufficient  nitric  acid  or  sodium  hydroxide  solution,  as  required, 
to  finally  leave  the  solution  slightly  acid.  Proceed  with  this 
solution  (pouring  it  into  sodium  hydroxide  solution,  etc.)  as 
described  in  the  Method  for  Ores  above. 


CHAPTER  XXX. 

ZINC. 

1.  The  following  method,  developed  by  the  writer,  for  the 
technical  estimation  of  zinc  in  ores,  etc.,  is  of  general  but  not 
of  universal  application.     Ordinarily,  however,  almost  the  only 
source  of  trouble  likely  to  be  encountered  is  the  preliminary 
decomposition  of  the  ore.     The  method  as  described  is  applicable 
to  the  usual  run  of  mixed  sulphide  ores  and  many  oxidized  ores. 
When  the  decomposition  fails  or  is  doubtful,  the  operator  must 
note  the  fact  and  apply  the  proper  remedy.     Some  observations 
on  this  and  related  matters  are  given  below. 

2.  Author's  Method.^-Prepare  a  solution  of  potassium  ferro- 
cyanide  containing  21.55  grams  of  the  crystallized  salt  to  the 
liter.     Standardize    this    solution    as    follows:-    Weigh    carefully 
about  0.2  gram  of  pure  zinc  into  an  8-oz.  flask  and  add  10  cc. 
of  strong  hydrochloric  acid  (sp.  gr.   1.20).     When  the  zinc  has 
dissolved,  dilute  with  about  25  cc.  of  water,  add  a  few  drops  of 
litmus  solution  as  an  indicator,  and  make  slightly  alkaline  with 
ammonia.     Again   acidify   slightly   with   hydrochloric   acid   and 
then  add  3  cc.  of  the  strong  acid  in  excess.     Dilute  now  to  about 
250  cc.  with  hot  water  and  heat  nearly  to  boiling.    Titrate  with 
the  f errocyanide  solutionjjas  follows :  Pour  about  two- thirds  of  the 
zinc  solution  from  the  flask  into  a  4oo-cc.  beaker.     Run  the 
f  errocyanide  solution  from  the  burette  into  this  portion,  a  few 
cubic  centimeters  at  a  time,  until  a  drop,  when  removed  and 
tested  on  a  porcelain  plate  with  a  drop  of  a  15  per  cent,  solution 
of  uranium  nitrate,  shows  a  brown  tinge.     Now  add  more  of  the 

284 


ZINC.  285 

zinc  solution  from  the  flask  and  continue  the  titration  more 
cautiously  until  the  end-point  is  again  passed.  Proceed  thus, 
adding  more  of  the  reserved  portion  in  such  amounts  as  may 
appear  advisable,  passing  the  end-point  each  time  with  greater 
caution.  Finally,  add  the  last  of  the  reserved  portion,  and  then, 
to  save  rinsing  out  the  flask,  pour  a  large  part  of  the  solution 
back  into  it  again  and  then  empty  it  once  more.  From  this  point 
finish  the  titration  very  carefully,  ordinarily  by  testing  after 
each  addition  of  two  drops.  Instead  of  using  a  single  drop  of 
the  zinc  solution  for  the  test,  the  reaction  is  sharper  if  a  quantity 
equivalent  to  several  drops  be  taken.  If  this  is  done  only  near 
the  end  of  the  titration  the  amount  of  zinc  lost  thereby  will  be 
insignificant.  J^A  convenient  way  of  making  the  test  is  to  use 
a  medicine-dropper  and  place  a  single  drop  of  the  uranium 
solution  in  each  depression  of  the  test-plate  at  the  outset.  By 
using  a  glass  tube  instead  of  a  rod  for  a  stirrer,  any  desired 
quantity  of  the  solution  can  be  quickly  removed  for  a  test.  When 
the  final  brown  tinge  is  obtained,  note  the  reading  of  the  burette, 
and  then  wait  a  minute  or  two  and  observe  if  one  or  more  of  the 
preceding  tests  do  not  also  develop  a  color.  The  end-point  is 
always  passed  by  a  test  or  two  and  the  burette  reading  must  be 
corrected  accordingly.  A  further  correction  must  also  be  made 
for  the  amount  of  ferrocyanide  required  to  produce  a  color  under 
the  same  conditions  when  no  zinc  is  present.  This  is  ordinarily 
i  drop,  i  cc.  of  the  standard  solution  will  equal  about  0.005 
gram  of  zinc,  or  in  the  case  of  ores,  about  i  per  cent,  when  0.5 
gram  is  taken  for  assay.  ^ 

3.  Regular  Method  for  Ores. — A  modification  of  the  method 
of  decomposition  described  below  is  sometimes  necessary.  Some 
ores  require  a  more  or  less  prolonged  treatment  with  hydrochloric 
acid,  to  insure  complete  decomposition  of  oxides,  before  adding 
nitric  acid.  Ores  that  gelatinize  should  be  mixed  with  a  little 


286  TECHNICAL  METHODS   OF   ORE  ANALYSIS. 

water  before  adding  any  acid,  and  then  the  acid  added  while 
agitating  the  flask,  to  prevent  setting  or  caking.  This  is  to  be 
followed  by  occasional  agitation  during  decomposition.  Other 
cases  will  be  referred  to  later. 

Weigh  0.5  gram  of  the  ore  into  an  8-oz.  Erlenmeyer  flask. 
Add  5  cc.  of  strong  hydrochloric  acid  and  10  cc.  of  strong  nitric 
acid.  Boil  gently  until  only  a  few  cubic  centimeters  of  liquid 
remain,  but  not  to  dryness  in  any  case.  Remove  from  the  heat 
and  add  12  cc.  of  strong  nitric  acid  and  5  grams  (usually  measured) 
of  potassium  chlorate.  (Mallinckrodt's  "Pure  Granular"  is 
convenient  for  measuring.)  Replace  the  flask  over  a  gentle  heat 
and  run  just  to  dryness.  If  the  mixture  shows  a  tendency  to 
"  bump,"  use  a  small  watch-glass  cover  raised  slightly  on  one 
side  with  a  bit  of  bent  glass  tubing,  to  allow  escape  of  vapors, 
removing  it  again  when  the  danger  is  passed.  The  raising  is 
unnecessary  if  the  flask  has  a  lip.  Hard  dryness  is  unnecessary 
except  when  gelatinous  silica  is  present,  and  even  in  this  case 
there  should  be  no  overheating  or  fusing  of  the  salts.  With  other 
ores  it  is  sufficient  to  run  just  to  dryness  and  remove  at  once 
from  the  heat.  As  soon  as  sufficiently  cool  add  35  cc.  of  a 
prepared  ammoniacal  solution  and  heat  to  boiling.  This  solution 
is  made  by  dissolving  200  grams  of  commercial  ammonium 
chloride  in  a  mixture  of  500  cc.  of  strong  ammonia  (sp.  gr.  0.90) 
and  750  cc.  of  water.  Boil  the  contents  of  the  flask  very  gently 
for  a  minute  or  two,  or  until  disintegration  of  the  residue  is  com- 
plete, and  then  add  saturated  bromine  water  and  continue  the 
boiling  for  a  short  time.  The  amount  of  bromine  water  to  add 
depends  upon  the  quantity  of  manganese  apparently  present,  as 
shown  by  the  deep  brown  color  of  the  residue,  All  the  manganese 
is  precipitated  by  the  mixture  of  nitric  acid  and  potassium  chlorate, 
but  on  evaporating  to  dryness,  some  of  the  manganese  is  again 
reduced  to  the  protoxide  form  and  becomes  more  or  less  soluble. 


ZINC.  287 

With  ores  showing  little  or  no  manganese  10  cc.  of  bromine  water 
are  sufficient,  and  25  cc.  will  usually  suffice  in  any  case.  Now 
filter  the  hot  solution  through  an  n-cm.  filter  into  a  4co-cc. 
beaker.  I  have  found  that  in  most  cases  the  liquid  runs  through 
much  more  rapidly  if  a  small  wad  of  absorbent  cotton  is  placed 
in  the  apex  of  the  filter  and  wetted.  Wash  out  the  flask  with  hot 
water.  A  slight  residue  adhering  to  the  flask  may  be  disregarded; 
a  larger  residue  that  cannot  be  removed  with  a  rubber-tipped 
rod  may  be  treated  as  follows:  Add  about  2  cc.  of  strong  hydro- 
chloric acid  to  dissolve  it,  and  then,  without  diluting  the  solution, 
add  5  cc.,  or  an  excess,  of  strong  ammonia  and  rinse  into  the 
filter.  Any  traces  of  manganese  not  precipitated  by  the  ammonia 
are  usually  negligible.  Wash  the  residue  on  the  filter  ten  times 
with  a  nearly  boiling  ammonium  chloride  mixture,  which  may 
be  contained  in  the  wash-bottle  described  on  page  9.  To  make 
the  ammonium  chloride  mixture,  dissolve  100  grams  of  commercial 
ammonium  chloride  in  water,  add  50  cc.  of  strong  ammonia  and 
dilute  to  i  liter.  Add  a  little  litmus  solution  to  the  filtrate  as  an 
indicator  and  then  cautiously  neutralize  with  strong  hydrochloric 
acid,  finally  adding  3  cc.  in  excess.  When  there  is  sufficient 
copper  present  to  act  as  an  indicator  the  litmus  may  be  omitted. 
Dilute  the  liquid,  if  necessary,  to  about  200  cc.  with  hot  water, 
heat  nearly  to  boiling,  and  add  50  cc.  of  saturated  hydrogen 
sulphide  water.  The  mixture  is  now  ready  for  titration.  Pour 
about  one-third  of  the  liquid  into  a  beaker  as  a  reserve  and 
conduct  the  titration  as  described  for  the  standardization  of  the 
ferrocyanide,  adding  portions  of  the  reserve  as  the  end-point  is 
successively  passed.  In  correcting  for  the  final  reading  of  the 
burette,  it  is  usually  sufficient  to  deduct  for  as  many  tests  as 
show  a  brown  tinge  and  one  drop  additional.  This  is  shown  by 
running  a  blank  test,  adding  the  ferrocyanide  one  drop  at  a 
time  and  making  a  test  after  each  drop.  In  the  course  of  a 


288  TECHNICAL    METHODS  OF  ORE    ANALYSIS. 

minute  a  brown  tinge  will  show  in  all  the  tests  except  the  first. 
Multiply  the  number  of  cubic  centimeters  used  by  the  percentage 
value  of  i  cc.  to  obtain  the  per  cent,  of  zinc  in  the  ore. 

4.  Ordinarily,   any  sulphides  precipitated  by  the   hydrogen 
sulphide   water  need  not  be  filtered   off,   as   the  discoloration 
produced  by  even  10  per  cent,  of  copper,  for  instance,  does  not 
too  badly  mask  the  uranium  test.     With  a  large  amount  of 
copper  present  the  procedure  may  be  as  follows:    After  adding 
an  excess  of  3  cc.  of  strong  hydrochloric  acid  to  the  filtrate  and 
diluting  it  to  about  200  cc.  with  hot  water,  pass     in  hydrogen 
sulphide  gas  to  saturation.     Filter  through  an  n-cm.  filter  and 
wash  the  precipitate  thoroughly  with  hot  water.     If  a  little  copper 
oxidizes  and  runs  into  the  filtrate  it  will  do  no  harm,  as  it  is 
immediately  reprecipitated  as  sulphide.     Heat  the  filtrate,  which 
should  have  a  final  volume  of  about  250  cc.,  nearly  to  boiling, 
and  titrate  as  usual. 

5.  Notes. — a.  It  is  not  sufficient  to  wash  the  residue  of  ferric 
hydroxide,  etc.,  simply  with  hot  water.     An  appreciable  amount 
of  zinc  is  likely  to  be  retained  unless  the  residue  is  thoroughly 
washed  with  the  hot  ammoniacal  solution  prescribed.     A  direct 
test  with  a  40  per  cent,  zinc  ore  showed  a  retention  of  1.27  per 
cent.,  which  was  afterward  easily  washed  out  with  the  ammo- 
niacal solution. 

b.  The  use  of  granulated  test  lead  as  a  precipitant  for  copper 
is   not  recommended.     Lead  acts   more  slowly  than   hydrogen 
sulphide,  sometimes  fails  to  entirely  remove  the  copper,   and, 
unless  the  precaution  of  a  special  procedure  be  adopted,  will 
always  produce  a  solution  with  an  unknown  and  variable  degree 
of  acidity,  thus  influencing  the  end-point.     For  a  method  using 
test  lead  see  8. 

c.  Metallic  aluminum  appears  to  be  entirely  unsuitable  for 
precipitating  the  copper,  unless  the  aluminum  which  goes  into 


ZINC.  289 

solution  is  subsequently  removed.  Aluminum  salts  affect  the 
titration  and  produce  incorrect  results.  In  carefully  conducted 
experiments  I  have  always  found  this  to  be  the  case,  under  my 
usual  working  conditions. 

d.  Even  when  the  zinc  contents  of  a  solution  are  approximately 
known,  it  is  not  advisable,  in  the  titration,  to  omit  working  with 
a  reserve  portion  and  proceeding  in  the  regular  manner.     The 
reaction  between  the  ferrocyanide  and  the  zinc  may  be  varied, 
at  least  temporarily,  by  varying  the  conditions,  and  a  false  end- 
point  may  be  obtained  by  working  too  rapidly. 

e.  Cadmium    is    not    completely    precipitated    by    hydrogen 
sulphide  from  a  hydrochloric  acid  solution  containing  consider- 
able alkali  chloride.     In  the  regular  method  (and  likewise  the 
alternate    and    test    lead  methods),  therefore,  cadmium  is  to  a 
greater  or  less  extent  counted  as  zinc,  small  amounts  not  being 
precipitated   at   all   by   the   hydrogen   sulphide.     Theoretically, 
100  Cd  =  8y.3  Zn.     (Actually,  about  62  Zn. — Waring.) 

/.  Arsenic,  when  present  in  large  amount,  may  make  trouble 
by  retaining  iron  in  the  ammoniacal  solution  filtered  from  the 
residue.  No  attention  need  be  paid  to  arsenic  unless  its  presence 
in  excess  is  thus  indicated.  In  such  a  case  begin  anew  and  give 
the  ore  the  following  preliminary  treatment:  Dissolve  the  ore  in 
the  usual  way,  but  use  an  8-oz.  copper  flask  instead  of  an  Erlen- 
meyer.  Boil  the  solution  nearly  to  dryness,  then  add  10  cc.  of 
strong  hydrochloric  acid  and  boil  until  it  is  half  gone  (to  expel 
nitric  acid).  Now  add  about  4  cc.  of  a  solution  of  i  gram  of 
sulphur  in  5  cc.  of  bromine  and  boil  gently  for  a  few  moments. 
Then  add  4  cc.  of  strong  sulphuric  acid  and  boil,  by  manipulating 
the  flask  over  a  free  flame,  until  it  is  nearly  all  driven  off.  The 
arsenic  will  thus  be  sufficiently  expelled.  Cool,  add  10  grams 
of  ammonium  chloride  and  20  cc.  of  water  and  finish  the  assay 
as  described  in  6. 


290  TECHNICAL   METHODS  OF  ORE   ANALYSIS. 

g.  The  opinion  seems  to  be  very  common  that  gelatinous 
silica,  unless  well  dehydrated,  is  liable  to  combine  with  and 
retain  some  of  the  zinc  on  the  addition  of  the  ammoniacal  extrac- 
tion solution.  My  own  experiments  have  invariably  indicated 
that  this  is  not  the  case.  A  large  amount  of  gelatinous  silica 
may  hold  some  zinc  mechanically  and  thus  render  its  complete 
extraction  and  the  thorough  washing  of  the  residue  more  difficult. 
The  partial  dehydration  obtained  by  following  the  regular  method 
is  usually  quite  sufficient  to  overcome  this  trouble. 

6.  Alternate   Method. — I  have  observed  that  in  the  presence 
of  a  large  excess  of  ammonium  chloride,   ammonia  will  pre- 
cipitate iron  entirely  free  from  zinc.     This  fact  may  be  applied 
to  the  assay  of  an  ore  as  follows : 

Treat  0.5  gram  in  an  8-oz.  copper  flask  with  5  cc.  of  strong 
hydrochloric  acid  and  10  cc.  of  strong  nitric  acid  and  boil  to 
pastiness.  The  final  use  of  5  cc.  of  strong  sulphuric  acid  is 
advisable  if  gelatinous  silica  separates.  In  this  case  boil  until 
the  sulphuric  acid  is  nearly  gone — best  by  manipulating  the  flask 
over  a  free  flame.  Cool  sufficiently,  add  10  grams  of  ammonium 
chloride  and  20  cc.  of  water  and  boil  the  mixture  to  effect  solution 
of  everything  soluble.  If  basic  salts  remain,  add  a  few  drops  of 
hydrochloric  acid  to  dissolve  them.  When  the  solution  is  clear, 
remove  from  the  heat,  add  strong  ammonia  water  in  about  5  cc. 
excess,  then  20  cc.  of  saturated  bromine  water  and  boil  for  a  few 
minutes.  If  the  blackish  brown  color  of  the  precipitate  indicates 
much  manganese,  add  more  bromine  water  to  insure  its  complete 
precipitation,  and  again  boil.  In  doubtful  cases  test  the  nitrate 
with  bromine  water.  Filter  and  finish  as  in  the  regular 
method  (3). 

7.  Particular  pains  must  be  taken  to  remove  all  manganese 
with   the  bromine   water,   since  none  is   separated   during   the 
decomposition,  as  in  the  regular  method.     When  the  amount 


ZINC.  251 

of  manganese  present  is  in  excess  of  a  few  per  cent,  it  is  not  safe 
to  precipitate  it  with  bromine,  since  it  is  liable  to  carry  down 
an  appreciable  quantity  of  zinc  as  manganite  (xvm,  12).  In 
such  a  case  I  would  not  advise  the  use  of  the  alternate  method.  • 

8.  Method    Using  Test-lead  to  Precipitate  Copper.* — Begin 
as  in  the  regular  method    3).     Use  hydrogen  peroxide  (6  cc.  or 
more)  instead  of  bromine  water  to  precipitate  the  manganese. 
(Bromine  and  its  compounds  are  more  difficult  to  subsequently 
remove.)     Boil  for  several  minutes  to  expel  the  excess  of  per- 
oxide.    Filter  and  wash  as  usual.     Make  the  nitrate  very  slightly 
acid  with  hydrochloric  acid,  using  methyl  orange  as  indicator. 
Add  about  20  grams  of  granulated  test-lead,  cover  the  beaker, 
and  boil  until  all  the  copper  is  precipitated,  i.e.,  until  the  solution 
has  become  perfectly  colorless  and  then  a  little  longer.     Dilute 
with  hot  water  to  about  250  cc.,  add  3  cc.  of  strong  hydrochloric 
acid  and  i  cc.  of  a  50  per  cent,  solution  of  sodium  thiosulphate, 
and  titrate  as  usual  at  an  initial  temperature  of  about  85°  C., 
using  the  uranium  indicator  and  making  the  proper  deductions 
as  in  the  regular  method. 

To  standardize  the  ferrocyanide  solution,  dissolve  about 
0.200  gram  of  zinc  in  10  cc.  of  i  :2  hydrochloric  acid,  add  7  grams 
of  ammonium  chloride,  make  alkaline  with  ammonia  and  then 
reacidify  slightly  with  hydrochloric  acid,  using  methyl  orange  as 
indicator.  Add  3  grams  of  test-lead,  heat  to  boiling,  dilute  to 
about  250  cc.  with  hot  water,  add  3  cc.  of  strong  hydrochloric 
acid  and  i  cc.  of  a  50  per  cent,  solution  of  sodium  thiosulphate 
and  titrate  as  just  described. 

9.  Treatment    of  Refractory  Ores,  etc. — No   exact   line   of 
treatment  can  be  prescribed   for  this  class   of  material.     The 
following  will  usually  suffice:    Begin  according  to  the  regular 

*  Method  used  by  Mr.  Chas.  S.  Curtis,  U.  S.  Assayer,  in  the  U.  S.  Customs 
Assay  Office,  Kansas  City,  Mo. 


292  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

method  (3).  As  soon  as  decomposition  is  as  complete  as  possible, 
dilute  somewhat  and  filter  from  the  insoluble  residue,  washing 
the  latter  with  hot  water.  Receive  the  filtrate  in  an  8-oz.  Erlen- 
meyer  flask  and  allow  it  to  concentrate  considerably  while  treat- 
ing the  residue.  If  the  residue  is  likely  to  contain  lead,  wash  it 
next  with  the  hot  sodium  acetate  solution  used  in  the  lead  assay 
(xvi,  i),  and  then  thoroughly  with  hot  water  to  remove  the 
sodium  acetate,  rejecting  these  filtrates.  Ignite  the  washed 
residue  at  a  low  temperature  in  a  platinum  dish  to  remove  the 
filter  paper.  Cool,  add  equal  parts  of  strong  hydrochloric  and 
hydrofluoric  acids,  and  digest  on  a  water-bath  until  solution  is 
complete,  adding  more  acids  if  necessary.  Finally,  evaporate  to 
small  bulk  and  then  add  more  hydrochloric  acid  and  evaporate 
again  to  small  bulk  to  remove  most  of  the  hydrofluoric  acid.  Wash 
this  solution  into  the  main  portion  which  is  concentrating.  Boil 
the  combined  solutions  to  small  bulk,  add  10  cc.  of  strong  nitric 
acid  and  boil  nearly  todryness.  Now  add  12  cc.  of  strong  nitric 
acid  and  5  grams  of  potassium  chlorate  and  continue  as  in  the 
regular  method. 

Sometimes  the  ore  or  other  material  may  be  treated  at  the 
outset  with  hydrochloric  and  hydrofluoric  acids,  in  platinum,  as 
just  described,  for  the  residue. 

The  washed  insoluble  residue  may  also  be  fused  with  alkali 
carbonate,  either  alone  or  mixed  with  borax  glass,  the  melt 
disintegrated  with  water,  and  the  mixture  transferred  to  the 
flask  containing  the  main  solution,  finishing  as  above. 

10.  Modification  to  Avoid  Cadmium. — If  it  be  desired*  to 
avoid  the  influence  of  cadmium,  either  of  the  following  methods 
may  be  adopted: 

Method  No.  i.  —  Begin  by  either  the  regular  or  alternate 
method  and  proceed  as  usual  until  the  filtered  ammoniacal  solu- 
tion is  obtained.  To  this  filtrate  add  a  few  cubic  centimeters 


ZINC.  293 

of  strong  ammonium  sulphide  solution.  It  is  usually  unneces- 
sary to  add  more  than  is  required  to  convert  to  sulphides  all  the 
cadmium  and  lead  present.  Stir  the  mixture,  and  then  add  3 
grams  of  potassium  cyanide,  either  as  the  coarsely  crushed  solid 
or  in  strong  solution.  Stir  the  mixture  until  all  the  zinc  sulphide 
has  dissolved,  allow  to  stand  a  short  time  for  the  cadmium  to 
separate,  and  then  filter.  Copper  goes  into  solution  with  the 
zinc,  while  cadmium  and  lead  remain  insoluble.  As  the  former 
is  liable  to  clog  the  filter  badly,  it  is  best  to  make  use  of  Dittrich's 
paper-pulp  idea*  as  follows:  Place  one- half  of  a  Q-cm.  filter  in 
a  6-oz.  flask  together  with  a  little  hot  water.  Cork  the  flask  and 
shake  it  violently  until  the  paper  is  reduced  to  a  fine  pulp.  Pour 
this  mixture  into  an  n-cm.  filter  placed  in  a  funnel  and  allow 
the  water  to  drain  off.  Now  place  a  /po-cc.  beaker  under  the 
funnel  and  filter  the  cyanide  solution  through  the  paper  pulp. 
Wash  out  the  beaker  with  cold  water,  and  then  wash  filter  and 
precipitate  with  a  cold  2  per  cent,  solution  of  potassium  cyanide. 
Remove  the  filtrate  to  a  hood,  add  some  litmus  solution  as  an 
indicator,  and  acidify  with  strong  hydrochloric  acid,  finally 
adding  10  cc.  in  excess.  If  no  potassium  chlorate  is  present  add 
2-3  grams.  Cover  the  beaker,  and  boil  until  the  hydrocyanic 
acid  is  expelled  and  the  mixture  has  clarified.  Finally  remove 
from  the  heat,  again  add  some  litmus  solution,  neutralize  with 
ammonia,  and  then  reacidify  with  3  cc.  excess  of  strong  hydro- 
chloric acid.  Have  the  volume  of  the  solution  as  near  as  possible 
to  200  cc.  To  the  nearly  boiling  liquid  add  50  cc.  of  strong 
hydrogen  sulphide  water  and  titrate  as  usual. 

'Method  No.  2.  —  Begin  as  usual  for  the  Alternate  Method,, 
finally  boiling  with  8  cc.  of  strong  sulphuric  acid  until  half  of  the 
latter  is  expelled  —  best  by  manipulating  the  flask  over  a  free 
flame.  Cool,  add  25  cc.  of  water,  heat  to  effect  solution,  and  then 

*I,   12. 


294  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

add  a  piece  of  stout  sheet  aluminum,  about  if  in.  long  and  f  in, 
wide.  Boil  the  mixture  for  perhaps  10  minutes,  or  until  the  solu- 
tion is  reduced  and  any  copper  present  is  precipitated.  Remove 
from  the  heat,  dilute,  add  litmus  solution  as  indicator,  and  then 
make  slightly  alkaline  with  ammonia.  Now  make  faintly  acid 
with  dilute  sulphuric  acid  (i :  4),  and  then  add  5  cc.  in  excess. 
Add,  now,  25  cc.  of  strong  hydrogen  sulphide  water.  This  will 
precipitate  any  remaining  traces  of  copper  and  also  ensure  the 
complete  precipitation  of  the  cadmium.  Filter,  washing  with  cold 
water  and  receive  the  filtrate  in  a  i2-oz.  flask.  Boil  the  solution 
until  the  hydrogen  sulphide  is  expelled,  then  add  5  cc.  of  strong 
nitric  acid  to  oxidize  the  iron,  and  continue  the  boiling  until 
the  solution  is  reduced  to  a  bulk  of  50  cc.  or  less.  Now  add 
10  grams  of  ammonium  chloride,  and  when  it  has  dissolved  add 
ammonia  in  about  5  cc.  excess,  then  20  cc.  of  saturated  bromine 
water  and  finish  the  assay  as  described  for  the  alternate  method 
(6).  Do  not  omit  the  50  cc.  of  hydrogen  sulphide  water  at  the  end. 

ii.  Waring's  Zinc  Method. — This  method  depends  upon  the 
separation  of  the  zinc  from  manganese,  iron,  and  aluminum 
by  means  of  hydrogen  sulphide,  under  slight  pressure,  in  a  solu- 
tion very  slightly  acidified  by  formic  acid;  the  metals  of  the 
copper  group  having  been  previously  separated  by  metallic  iron 
or  aluminum  with  simultaneous  reduction  of  ferric  salts.  The 
operations  are: 

(i)  Solution. — The  calamine,  willimite,  franklinite,  blende, 
and  other  soluble  minerals,  or  ores  containing  them,  are  decom- 
posed by  hydrochloric  acid  or  aqua  regia,  with  subsequent  treat- 
ment and  evaporation  with  an  excess  of  hydrochloric  or  sulphuric 
acid  to  thoroughly  eliminate  nitrous  compounds.  If  zinc  spinels 
or  aluminates  are  present,  the  insoluble  residue  must  be  fused 
with  a  mixture  of  sodium  carbonate  and  borax  glass,  the  fused 
mass  dissolved  and  the  solution  added  to  the  main  one.  If  much 


ZINC.  295 

silica  is  present,  spinels  are  decomposed  by  fusion  with  sodium 
carbonate  in  a  platinum  crucible,  any  lead  sulphate  present  having 
been  extracted  by  ammonium  acetate.  In  the  absence  of  silica  or 
boric  acid,  the  spinels  cannot  be  decomposed  by  fusion  with  sodium 
carbonate  alone.  In  such  a  case  they  can  be  decomposed  by  pro- 
longed fusion  with  an  alkali  bisulphate.  Silicates,  such  as  cinders 
from:  oxide  furnaces,  unchilled  slags,  and  some  natural  silicates 
undecompo sable  by  acids,  must  be  fluxed  or  cintered  with  sodium 
carbonate  before  treatment  with  hydrochloric  acid.  It  is  not 
necessary,  in  any  case,  to  evaporate  to  dryness  to  separate  silica — 
it  can  be  filtered  off  in  the  gelatinous  state.  This  can  be  done 
very  rapidly,  after  dilution  with  water,  when  the  gelatinization 
has  reached  a  maximum  and  before  dehydration  has  begun. 
The  gelatinous  silica  at  this  stage  will  not  retain  any  traces  of 
metals  after  a  few  washings. 

(2)  Reduction. — To* avoid  the  effects  of  reactions  like 

2FeCl3+H2S=  2FeCl2  +  2HCl  +  S, 

and  at  the  same  time  to  remove  copper,  silver,  and  bismuth 
before  precipitating  with  hydrogen  sulphide,  the  filtered  solu- 
tion, made  fairly  acid  with  hydrochloric  or  sulphuric  acid,  is 
boiled  for  fifteen  or  twenty  minutes  with  a  strip  of  clean  sheet 
iron  or  steel.  By  this  treatment  all  the  metals  likely  to  be  pre- 
cipitated with  zinc  as  sulphides  are  separated,  except  cadmium, 
which  is  not  in  the  least  degree  reduced  by  metallic  iron. 

Mr.  G.  C.  Stone  has  suggested  the  use  of  metallic  aluminum 
for  the  reduction.  This  has  the  advantage  of  separating  cadmium 
and  lead  along  with  the  other  metals  of  the  copper  group,  since 
both  are  completely  precipitated  by  aluminum  from  a  rathei 
strongly  acid  boiling  solution  of  sulphates  or  chlorides,  so  that 
when  zinc  only  is  to  be  determined,  the  subsequent  operations 
are  very  much  shortened. 

Reduction  may  also  be  effected  by  means  of  sodium  sulphite 


296 


TECHNICAL  METHODS  OF   ORE  ANALYSIS- 


or  thiosulphate,  when  copper,  or  copper  and  aluminum  are  to 
be  determined  from  the  same  weighed  portion. 

The  reduction  is  followed  by  nitration,  the  nitrate  being 
received  in  a  flask  of  about  3oo-cc.  capacity. 

(3)  Neutralization. — Add  to  the  nitrates  a  drop  of  methyl 
orange,  then  run  in,  from  a  pipette,  a  rather  dilute  solution  of 
sodium  hydroxide,  meanwhile  constantly  agftating  the  contents 
of  the  flask  with  a  swirling  motion,  until  the  pink  color  barely, 
but  permanently,  changes  to  a  light  yellowish  tint  and  the  cloudi- 


FlG.    20. 

ness,  due  to  the  separation  of  hydroxides,  fails  to  clear  up 
entirely.  Then  add,  drop  by  drop,  enough  50  per  cent,  formic 
acid  (sp.  gr.  1.12)  to  just  restore  the  permanent  pink  color,  and 
add  up  to  half  a  cubic  centimeter  additional.  Dilute  the  solu- 
tion to  200  or  250  cc.  (or  so  that  it  will  contain  not  more  than 
0.15  to  0.20  gram  of  metallic  zinc  in  100  cc.)  and  heat  to  about 
80°. 

(4)  Precipitation. — A  rubber  stopper,  through  which  passes 
the  delivery-tube  from  a  source  of  supply  of  hydrogen  sulphide,* 

*  The  apparatus  used  by  Waring  is  shown  in  Fig.  20.  It  is  adapted  from  that 
of  C.  A.  Brewer.  The  lower  end  of  separatory-funnel  is  somewhat  contracted 
and  extends  to  txrttom  of  coarse  shot  upon  which  rests  the  FeS. 


ZINC.  297 

is  loosely  placed  in  the  neck  of  the  flask  and  a  moderately  rapid 
stream  of  gas  allowed  to  pass  through  the  hot  liquid.  When 
the  precipitation  of  zinc  sulphide  is  well  under  way,  the  stopper 
is  pushed  in  tightly.  Absorption  of  the  gas  ceases  when  all 
the  zinc  is  precipitated;  the  precipitate  settles  quickly,  and  the 
gas  pressure  rises  rapidly  when  the  operation  is  completed, 
When  several  precipitations  arc  to  be  made  at  the  same  time,* 
the  flasks  are  arranged  in  succession  in  the  usual  manner  and 
the  first  is  removed  when  the  precipitation  is  well  started  in 
the  third,  and  so  on,  changing  the  gas  connections  as  required. 
The  outlet  from  the  last  flask  is  not  closed  until  the  precipitation 
is  partially  completed  therein.  Numerous  experiments  have 
shown  that  zinc  can  be  completely  precipitated  and  separated  from 
iron,  manganese,  and  alumina  under  the  conditions  named,  by 
the  passage  of  only  a  very  little  more  than  the  amount  of  hydrogen 
sulphide  theoretically  required.  The  use  of  a  large  excess  is 
therefore  unnecessary  and  is  also  undesirable. 

(5)  Treatment  oj  the  Precipitate. — When  the  preceding  opera- 
tions have  been  properly  performed,  the  precipitated  zinc  sul- 
phide will  be  pure  white,  pulverulent,  and  very  easily  filtered 
and  washed.  Hot  water  only  need  be  used  for  washing,  no  zinc 
will  dissolve  or  pass  through  the  filter,  as  is  the  case  with  the 
slimy  zinc  hydrosulphide  precipitated  from  cold  solutions  in 
the  usual  manner.  Pour  the  "contents  of  the  flask  upon  a  filter 
at  once  and  wash  with  hot  water.  Spread  the  filter  with  its 
contents  upon  a  large  watch-glass  or  on  the  inner  wall  of  a  capa- 
cious beaker,  and  wash  the  precipitate  into  the  bottom  of  the 
beaker  by  a  jet  of  hot  water.  Wash  the  precipitating-flask  and 
the  lower  end  of  the  gas  delivery-tube  with  10  cc.  of  strong  hydro- 
chloric acid,  followed  by  hot  water,  pouring  the  acid  and  washings 
successively  over  the  washed  filter  on  to  the  precipitate  in  the 
beaker.  When  the  volume  of  the  acid  solution  has  reached 


298  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

125  to  130  cc.  the  solution  is  wanned  gently  to  dissolve  the  zinc 
sulphide  completely. 

When  cadmium  is  also  present,  (i.e.,  when  the  reduction 
has  been  effected  by  metallic  iron),  the  zinc  sulphide  will  dissolve 
completely  before  any  cadmium  sulphide  is  dissolved.  By 
practice  and  experience,  the  point  when  all  the  zinc  is  dissolved 
and  only  the  brilliant  yellow  cadmium  sulphide  remains,  can 
easily  be  distinguished.  The  solution  is  then  further  diluted 
with  an  equal  volume  of  hydrogen  sulphide  water,  allowed  to 
settle  and  the  cadmium  sulphide  filtered  off  and  estimated  in 
the  usual  way  by  warming  with  acid  ferric  sulphate  and  titrating 
with  permanganate.  The  iron  equivalent  of  the  permanganate 
used  multiplied  by  1.006  equals  the  cadmium.  Properly  per- 
formed, the  result  is  accurate  *  (Waring). 

The  solution  of  zinc  sulphide  in  dilute  hydrochloric  acid  is 
heated  to  60°  or  more,  made  up  to  200  or  250  cc.  with  hot  water, 
d  little  ammonium  chloride  added,  and  it  is  ready  for  titration 
with  ferrocyanide  (see  2). 

The  method  of  separating  zinc  by  hydrogen  sulphide  from 
nickel,  cobalt,  and  manganese,  recommended  by  Fresenius,f 
is  not  applicable  when  iron  is  present,  as  iron  is  thrown  down 
by  hydrogen  sulphide  in  the  presence  of  sodium  acetate. 

12.  Modification.  For  Low-grade  Zinc  Ores,  Slags,  Fur- 
nace Residues,  etc.,  and  for  all  purposes  wherein  it  is  required 
to  determine  small  amounts  of  zinc  accurately. 

Proceed  exactly  according  to  the  method  just  described  until 
the  zinc  sulphide  precipitate  has  been  washed,  then,  instead  of 
dissolving  the  precipitate,  dry  and  ignite  it  carefully  in  a  clean 

*  Treadwell  says  (Anal.  Chem.,  Hall,  2d  Ed.,  II,  p.  167):  "It  is  not  possible 
to  precipitate  pure  cadmium  sulphide  from  acid  solutions  by  means  of  hydrogen 
sulphide;  the  precipitate  is  always  contaminated  with  a  basic  salt  (Cd2Cl2S  — 
Cd2SO4S,  etc.),  whether  the  precipitation  takes  place  in  cold  or  hot  solutions, 
whether  under  atmospheric  pressure  or  under  increased  pressure  (in  a  pressure- 
flask),  and  in  fact  the  amount  of  basic  salt  formed  increases  with  the  amount  of  free 
acid  present." 

t  American  edition,  sec.  160,  paragraphs  74  and  75. 


ZINC.  299 

muffle  without  separating  it  from  the  paper.  No  loss  of  zinc  will 
occur,  nor  will  basic  sulphate  be  formed,  if  the  wet  precipitate  is 
ignited  at  the  mouth  of  the  muffle  until  the  paper  is  consumed,  and 
the  oxidation  of  the  residue  is  then  conducted  at  a  low  temperature 
(about  450°)  until  at  the  last,  when  it  may  be  moved  back  to  where 
the  temperature  is  near  the  meltirg-point  of  silver. 

As  much  as  0.15  gram  cf  zinc  sulphide  can  be  completely 
oxidized  in  this  way  in  forty  to  sixty  minutes.  The  calcination 
may  be  effected  in  a  smooth  shallow  scorifier,  an  inch  and  a  half 
in  diameter,  from  which  the  calcined  oxide  can  be  brushed  into 
the  scale-pan  without  appreciable  loss.  Calculate  the  zinc  from 
the  ZnO  found  by  multiplying  by  0.8035. 

Waring' s  method  has  been  modified  both  by  its  author  and 
by  Dr.  H.  C.  P.  Weber  of  the  U.  S.  Bureau  of  Standards,  and 
the  following  scheme  including  the  changes  is  proposed  by  the 
Zinc  Committee  of  the  American  Chemical  Society. 

13.  Modified  Waring  Method.* — After  decomposing  the 
weighed  sample  by  acids  alone,  or  aided  by  fusion,  as  the  case 
may  require,  all  the  zinc  is  to  be  brought  into  solution  as  sulphate. 
If  nitric  acid  was  used  in  the  decomposition,  all  traces  of  it  must 
be  expelled  by  evaporation  with  hydrochloric  and  sulphuric 
acids  successively,  or  by  two  evaporations  with  sulphuric  acid, 
finally  to  abundant  evolution  of  SO3  fumes.  Dissolve  the  mass 
in  25  to  40  cc.  of  water  and  add  sufficient  sulphuric  acid  to  bring 
the  free  acid  in  the  solution  up  to  10  or  15  per  cent.  Introduce 
piece  of  heavy  sheet  aluminum  and  boil  10  minutes,  or  to  com- 
plete reduction.  Filter,  and  wash  through  a  filter  containing  a 
piece  of  aluminum  into  a  beaker  containing  a  stirring-rod  or 
strip  of  the  same  metal,  cool,  add  a  drop  of  methyl  orange,  and 
neutralize  carefully  with  sodium  bicarbonate  to  a  light  straw  colon 
Add,  dropwise,  dilute  formic  acid  (20  per  cent,  strength)  until 

*  Jour.  Am.  Chem.  Soc.,  XXIX,  265. 


300  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

the  pink  color  is  just  restored,  then  5  drops  more.  (Dilute  hydro- 
chloric acid,  i  part  strong  acid  to  6  parts  water,  may  be  sub- 
stituted for  formic  acid  when  ammonium  thiocyanate  *  is  to  be 
introduced.)  Dilute  to  about  100  cc.  for  each  o.i  gram  of  zinc 
possibly  present,  add,  if  much  iron  is  present,  2  to  4  grams 
ammonium  thiocyanate,  remove  the  strip  of  aluminum,  heat 
nearly  to  boiling,  and  saturate  with  hydrogen  sulphide.  Allow 
the  pure  white  zinc  sulphide  to  subside  for  a  few  minutes,  then 
filter  and  wash  with  hot  water.  Transfer  precipitate  and  filter 
to  a  capacious  beaker,  heat  with  8  or  10  cc.  of  strong  hydro- 
chloric acid  and  30  or  40  cc.  of  water,  until  the  zinc  is  all  in  solu- 
tion. Determine  the  zinc  as  pyrophosphate  containing  42.91 
per  cent,  zinc,  or  by  titration  with  ferrocyanide.  The  use  of 
ammonium  heptamolybdate  f  in  one  per  cent,  solution  as  an 
indicator,  instead  of  uranium  acetate  or  nitrate,  is  recommended, 
provided  all  free  hydrogen  sulphide  has  been  previously  expelled 
from  the  solution  by  heating.  If  a  blue  color  still  appears  in  the 
test  drop,  add  a  crystal  or  two  of  sodium  sulphite  to  the  zinc 
solution,  to  decompose  any  remaining  hydrogen  sulphide. 

14.  Notes.  —  Using  the  thiocyanate  modification  and  the 
ferrocyanide  titration,  I  have  found  the  above  very  accurate, 
except  that  cadmium  was  not  entirely  removed  —  at  least  in 
presence  of  copper.  To  conform  to  my  method  of  standard- 
ization proceed  as  follows:  Drop  filter  with  zinc  sulphide  into  a 
6-oz.  flask.  Cleanse  beaker  and  delivery  tube  with  25  cc.  of 
hydrochloric  acid  and  rinse  into  the  flask.  Boil  to  dissolve  the 
zinc,  disintegrate  the  filter  and  expel  all  hydrogen  sulphide.  Add 
a  little  litmus  solution  or  paper,  neutralize  with  ammonia,  and 
then  reacidify  with  3  cc.  excess  of  hydrochloric  acid.  Transfer 
to  a  400-cc.  beaker,  dilute  to  250  cc.  and  titrate  hot,  as  usual. 

*  Zimmermann,  Ann.  Chem.,  (Liebig),  99,  i. 
t  Nissenson  and  Kittembcil,  Chem.  Zeit.,  77  (1905),  951-955. 


ZINC.  301 

15.  Notes  by  Waring  and  Stone.  —  Under  the  conditions 
described  the  precipitation  of  cadmium  is  complete,  but  traces  of 
copper  remain  in  solution  unless  the  boiling  is  continued  for  a 
very  long  time;  this  prolonged  boiling  is  not  necessary  as  the 
copper  is  afterwards  precipitated  as  sulphide  with  the  zinc  and 
does  not  redissolve  with  the  latter. 

In  neutralizing,  if  the  solution  is  strongly  acid,  it  is  better  to 
nearly  neutralize  with  sodium  or  potassium  hydroxide  and 
finish  with  bicarbonate.  This  not  only  saves  time  but  lessens 
the  chance  of  loss  by  foaming. 

It  is  not  necessary  to  pass  the  hydrogen  sulphide  under  pres- 
sure if  the  solution  is  diluted  as  already  directed.  The  gas 
should  be  passed  through  the  solution  until  a  drop  of  the  liquid 
blackens  a  drop  of  cobalt  or  nickel  sulphate  or  chloride  made 
alkaline  with  ammonia.  After  a  little  experience  it  is  not 
necessary  to  make  even  this  test.  It  is  very  important  that  the 
zinc  solution  should  be  quite  hot  during  the  precipitation  of  the 
sulphide,  therefore  it  is  advisable  to  begin  nearly  at  the  boiling- 
point  and  to  pass  the  gas  rapidly.  If  the  heating  of  the  solution 
has  taken  much  time,  the  excess  of  formic  acid  may  volatilize  (if 
this  reagent  has  been  used).  In  such  cases  enough  more  must 
be  added  to  make  the  solution  acid. 

We  most  strongly  recommend  that  zinc  be  determined  gravi- 
metrically  by  weighing  as  pyrophosphate,  except  where  the 
operator  has  had  much  and  recent  practice  with  the  ferro- 
cyanide  titration.  While  the  latter  is  capable  of  giving  very 
accurate  results  it  will  only  do  so  when  all  the  conditions  are 
exactly  the  same  both  in  standardizing  and  during  the  final 
titration,  and  it  is  necessary  to  have  considerable  experience  with 
the  method  to  be  sure  of  accuracy. 

16.    Weighing    the    Zinc    as    Pyrophosphate.*  —  Filter    the 

*  Method  of  Geo.  C.  Stone.     W.  Geo.  Waring,  Jour.  Am.  Chem.  Soc.,  XXVI,  28. 


302  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

solution  of  the  zinc  sulphide  in  hydrochloric  acid  finally  obtained 
in  Waring's  Method  and  bring  the  filtrate  to  a  cold,  dilute  and 
slightly  acid  condition.  Now  add  a  large  excess  of  ammonium 
sodium  hydrogen  phosphate  and  then  neutralize  very  carefully 
with  ammonia,  adding  it  drop  by  drop,  finally  adding  a  drop  or 
two  in  excess.  Finally,  add  about  i  cc.  of  acetic  acid  and  warm 
gently  until  the  flocculent  precipitate  of  ZnNH4PO4  +  H2O 
has  settled  completely  as  a  dense  crystalline  powder.  Filter 
and  wash  with  hot  water. 

Dry  the  filter  and  precipitate,  separate  the  paper  and  burn  it, 
add  the  ash  to  the  residue  and  ignite  the  two,  gently  at  first, 
then  for  a  few  minutes  at  a  bright  red  heat.  Cool  and  weigh 
as  Zn2P2O7,  containing  42.77  per  cent,  of  zinc. 

The  flocculent  ZnNH4PO4  +  H2O  is  very  soluble  in  the 
mineral  acids  as  well  as  in  ammonia,  but  after  crystallization 
it  is  much  less  soluble  in  the  latter.  It  is  only  slightly  soluble 
in  acetic  acid;  an  excess  of  i  cc.  in  100  cc.  of  solution  does  not 
dissolve  an  appreciable  quantity.  It  is  somewhat  soluble  in  all 
ammonium  salts,  if  only  a  small  excess  of  phosphate  is  present. 
The  addition  of  i  cc.  of  a  10  per  cent,  solution  of  sodium  am- 
monium phosphate  for  each  0.005  gram  of  zinc  is  sufficient  to 
entirely  prevent  its  solution  in  ammonium  chloride  or  sulphate 
or  in  the  acetate  unless  the  latter  is  present  in  enormous  quantity. 
It  is,  however,  always  slightly  soluble  in  the  oxalate.  Therefore, 
for  very  accurate  work,  lime  and  magnesia,  if  present  in  the  zinc 
solution,  are  preferably  separated  together  as  phosphates,  after 
adding  a  large  excess  of  ammonia  and  reprecipitating;  then  the 
combined  filtrates  are  to  be  slightly  acidulated  and  proceeded 
with  as  above.  The  crystalline  zinc  ammonium  phosphate  is 
quite  insoluble  in  hot  or  cold  water. 


CHAPTER    XXXI. 

COMBINING    DETERMINATIONS. 

IT  is  an  ordinary  occurrence  for  the  technical  chemist  to 
have  to  determine  several  constituents  in  the  same  sample  of 
ore.  The  expert  operator  will,  of  course,  be  able  to  combine  his 
regular  methods  for  single  constituents,  whenever  possible  or 
convenient,  so  as  to  make  two  or  more  determinations  from  the 
same  weighed  portion  .of  ore,  and  thus  save  considerable  time. 
The  accuracy  of  the  work  is  sometimes  lessened  by  such  a  com- 
bination, and  its  adoption  will  then  depend  upon  the  rigor  of  the 
requirements. 

The  following  examples  are  perhaps  sufficient  to  show  how 
work  can  be  hastened  in  a  busy  laboratory,  using  only  technical 
methods.  Of  course,  by  the  tedious  operations  of  exact  analysis, 
many  constituents  can  sometimes  be  determined  from  the  same 
weighed  portion,  but  such  methods  are  not  under  consideration. 
Where  much  extra  manipulation  is  involved,  it  is  usually  not 
worth  while  to  work  by  a  combination  method. 

i.  Copper,  Lead  and  Insoluble. — Make  the  copper  as  usual 
(xm,  3),  but  take  the  precaution  to  cool  the  solution  before 
the  first  filtration  and  to  wash  the  lead  sulphate  residue  with 
dilute  sulphuric  acid.  Dissolve  the  lead  sulphate  on  the  filter 
with  the  usual  hot  sodium  acetate  solution  and  proceed  with 

3°3 


334  TECHNICAL  METHODS  OF   OJIE  ANALYSIS. 

the  filtrate  as  described  for  lead  (xvi,  4).  Thoroughly  wash  the 
residue  remaining  on  the  filter  with  .hot  water,  to  remove  the 
sodium  acetate,  and  .then  ignite  filter  and  contents  and  weigh 
as  insoluble  residue. 

2.  Zinc,  Iron  and  Insoluble. — Make  the  zinc  as  usual  (xxx, 
3).  The  iron  and  insoluble  residue  will  be  either  on  the  filter 
or  adhering  in  the  flask.  Rinse  the  precipitate  on  the  filter 
into  a  beaker  with  hot  water,  using  as  little  as  possible.  Add 
5  cc.  of  strong  hydrochloric  acid  and  warm  the  mixture  until 
the  ferric  hydroxide,  etc.,  has  dissolved.  Transfer  this  solution, 
and  any  insoluble  residue,  into  the  original  flask  and  again 
warm,  if  necessary,  to  dissolve  any  adhering  precipitate.  Now 
filter  through  the  same  filter  as  before,  thus  dissolving  any  pre- 
cipitate thereon,  receiving  the  filtrate  in  an  8-oz.  flask.  Wash 
flask  and  filter  with  hot  water  acidulated  with  a  few  drops  of 
hydrochloric  acid,  and  see  that  all  the  residue  is  transferred  from 
the  flask  to  the  filter,  using  a  rubber- tipped  bent  glass  rod,  if 
necessary,  to  detach  adhering  particles.  Concentrate  the  filtrate 
by  boiling,  if  too  bulky,  and  determine  the  iron  in  it  as  usual 
(xv,  31). 

The  insoluble  residue  is  now  ready  to  ignite  unless  it  is  liable 
to  contain  lead.  In  this  case  dissolve  out  the  lead  with  a  strong 
hot  solution  of  ammonium  chloride,  acidulated  with  hydrochloric 
acid,  or  employ  the  hot  sodium  acetate  solution  used  in  the  lead 
assay  (xvi,  i).  Finally,  wash  thoroughly  with  hot  water,  then 
ignite  filter  and  contents  and  weigh  as  usual. 

4.  Calcium  and  Magnesium. — It  is  evident  that  no  modifica- 
tions of  the  methods  described  are  necessary  in  this  case.     Simply 
proceed  as  for  CaO  (x,  i),  and  in  the  filtrate  from  the  calcium 
oxalate  determine  the  MgO  in  the  usual  manner  (xvn,  1,2). 

5.  Insoluble,  Iron,  Calcium    and    Magnesium. — Proceed  as 
for  insoluble  residue  by  any  appropriate  method  (xxiv,  2).     Wash 


COMBINING   DETERMINATIONS.  305 

the  filtered  residue  with  hot  water  slightly  acidulated  with  hydro- 
chloric acid  and  then  treat  it  as  in  3  above.  If  it  requires 
purification  from  lead,  do  not  add  the  resulting  filtrate  to  the 
original  filtrate. 

Proceed  with  the  original  filtrate  as  for  calcium  (x,  i),  and 
thus  obtain  the  iron  as  ferric  hydroxide,  the  calcium  and  magne- 
sium being  in  the  filtrate  (or  filtrates).  Determine  the  latter  as 
above  (4). 

If  the  ferric  hydroxide  is  small  in  amount,  dissolve  it  on  the 
filter  by  pouring  over  it  a  hpt  mixture  of  10  cc.  of  strong  hydro- 
chloric acid  and  20  cc.  of  water,  receiving  the  filtrate  in  an  8-oz. 
flask.  It  is  best  to  wash  larger  amounts  into  a  beaker  with  a 
little  hot  water,  add  5-10  cc.  of  hydrochloric  acid  and  warm 
until  the  iron  precipitate  has  dissolved,  pouring  the  solution 
through  the  filter  to  dissolve  what  remains  there.  Wash  the 
filter  with  hot  water  slightly  acidulated  with  .hydrochloric  acid. 
Concentrate  the  filtrate  by  boiling,  if  necessary,  and  determine 
the  iron  in  it  in  the  usual  manner  (xv,  31). 

6.  Copper  and  Iron. — Proceed  as  for  copper  by  the  iodide 
method  (xm,  3),  determining  the  copper  as  usual.     The  filtrate 
from  the  precipitated  copper  will  contain  the  iron  all  reduced, 
but  also  containing  hydrogen  sulphide.     Boil  the  solution  in  a 
flask  until  the  hydrogen  sulphide  is  completely  expelled,  then 
transfer  it  to  a  battery-jar  containing  some  cold  water,  dilute  to 
700  cc.  with  cold  water,  add  5  cc.  of  strong  sulphuric  acid  and 
titrate   with   permanganate,  as  described  in  xv,  8.     Of  course 
the  aluminum  used  should  be  practically  free  from  iron. 

It  will  be  observed  that  the  above  combinations  can  be  com- 
bined with  each  other  in  certain  cases,  for  instance, 

7.  Insoluble,  Lead,  Copper  and  Iron. — Proceed  as  in  i,  de- 
termining the  lead  and  insoluble  in  the  residue,  and  then  deter- 
mine the  copper  and  iron  in  the  filtrate  according  to  6. 


CHAPTER  XXXII. 

BOILER  WATER. 

FULL  directions  for  the  analysis  of  water  to  be  used  for  steam 
purposes  can  be  found  in  most  of  the  books  on  technical  analysis, 
and  it  is  not  intended  to  describe  an  elaborate  method  in  this 
work.  The  following  scheme  can  be  carried  out  very  quickly, 
and  is  sufficiently  accurate  in  most  cases: 

If  the  water  k  turbid,  allow  it  to  settle  or  filter  it  so  as  to 
remove  the  suspended  matter. 

i.  Total  Solids.  —  Evaporate  100  cc.  in  a  weighed  platinum 
dish  on  the  water-bath  to  dryness.  If  the  dish  is  too  small  to 
hold  ico  cc.  at  once,  measure  the  water  into  a  beaker  and  transfer 
it  to  the  dish  as  the  evaporation  proceeds.  A  loo-cc.  pipette 
is  most  convenient  for  the  measuring,  as  no  washing  out  is  neces- 
sary and  there  is,  therefore,  no  wash- water  to  evaporate.  After 
evaporation,  place  the  dish  and  residue  in  an  air-bath  and  heat 
at  150°  C.  for  thirty  minutes.  Cool  in  desiccator  and  weigh. 
2.  Organic  and  Volatile  Matter.  —  Hold  the  dish  contain- 
ing the  dry  residue  in  the  tongs  and  manipulate  it  over  a  Bunsen 
flame  so  as  to  burn  off  the  organic  matter  at  as  low  a  tempera- 
ture as  possible.  Sometimes  the  burned  residue  remains  dark 
owing  to  the  presence  of  manganese.  If  this  is  mistaken  fo: 

unburned  carbon  too  high  a  temperature  may  be  employed  ID 

306 


BOILER  WATER.  307 

attempting  to  consume  it  and  more  or  less  carbon  dioxide  may  be 
expelled  from  carbonates  in  consequence.  This  carbon  dioxide 
can  be  replaced  by  adding  a  little  CO2  water  and  evaporating  to 
dryness,  but  the  extra  trouble  is  hardly  worth  while,  as  the  pos- 
sible errors  of  this  determination  are  liable  to  make  it  unsatis- 
factory in  any  event.  The  result  obtained  is  seldom  used,  but  it 
sometimes  proves  useful  as  a  check.  After  the  ignition  cool  the  dish 
in  a  desiccator  and  weigh,  noting  the  loss  from  the  lasr  weight. 

3.  Conversion   to   Sulphates. — Add  sufficient  dilute  sulphuric 
acid  to  the   last  residue   in  the  dish  (a  few  drops  are  usually 
enough)  and  turn  the  latter  in  various  positions  so  that  the  acid 
will  come  in  contact  with  all  the  residue.     Note  whether  or  not 
an  effervescence  indicating  carbonates  is  produced,  as  knowledge 
on  this  point  may  prove  useful  later.     Heat  the  dish  cautiously 
so  as  to  expel  the  water  and  free  sulphuric  acid  and  then  raise 
the    temperature    sufficiently   to    decompose    any   iron    sulphate 
and   leave  ferric  oxide;   avoid  unnecessary  overheating  however. 
Cool  and  weigh  as  combined  Na2SC>4,  CaSO4,   MgSC>4,  Fe2Oa, 
and  SiC>2.     This  weight  will  be  used  in  the  calculation  of  results. 

4.  Silica. — Warm  the  sulphate   residue  with  sufficient  dilute 
hydrochloric  acid  to  dissolve  all  the  sulphates.     If  there  is  much 
ferric  oxide  it  is  best  to  warm  with  a  little  strong  acid  at  first 
until  it  has  dissolved.     Filter  through  a  small  ash  less  filter  and 
wash  with  hot  water.     Sometimes  it  is  a  good  plan  to  loosen 
any  insoluble  matter  on  the  sides  of  the  dish  with  a  rubber-tipped 
glass  rod  and  continue  the  heating  with  dilute  acid  to  make  sure 
that   all   sulphates   are   dissolved.     Return   the   filter  and   any 
insoluble  residue  to  the  dish  and  ignite.    After  cooling,  weigh 
as  SiC>2. 

5.  Ferric  Oxide,  etc. — Heat  the  filtrate  from  the  silica  nearly 
to  boiling  and  add  a  slight  excess  of  ammonia,  preceded,  if  man- 
ganese  is  possibly  present,  by  5  cc.  of  strong  bromine  water. 


308  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Bring  to  a  boil  and  then  allow  to  stand  over  a  low  flame  for  a 
short  time  for  the  precipitate  to  collect.  Finally,  filter  through 
a  small  ashless  filter,  wash  with  hot  water,  ignite  and  weigh, 
after  cooling,  as  Fe2Os.  The  amount  is  usually  so  small  that 
the  platinum  or  porcelain  crucible  used  for  the  ignition  need 
not  be  weighed,  but  the  ferric  oxide  transferred  directly  to  the 
scale-pan.  Only  in  rare  cases  where  Mn3O4  or  A12O3  are 
present  in  unusual  amount  is  it  necessary  to  make  any  special 
separation  of  these  substances. 

6.  Calcium  Oxide. — Heat  the  filtrate  from  the  ferric  hydroxide 
to  boiling,  add  sufficient  ammonium  oxalate  solution  and  allow 
to  stand,  hot,  till  the  precipitate  has  settled.     Filter,  wash  well 
with  hot  water,  and  determine  the  CaO  in  the  calcium  oxalate 
by  titration  with  potassium  permanganate,  as  in  x,  4. 

7.  Magnesium  Oxide.  —  Concentrate    the    filtrate    from    the 
calcium  oxalate  to  smaller  bulk  if  necessary,  and  then  precipitate 
the  magnesium  as  magnesium  ammonium  phosphate,  as  described 
in  xvn,  2,  finally  weighing  as  Mg2P2O7  and  calculating  to  MgO. 

8.  Alkalies. — For  the  purposes  of  this  analysis  it  is  usually 
sufficient  to  regard  the  alkalies  as  consisting  wholly  of  Na2O. 
The  amount  of  Na2O  is  determined  by  calculation  as  follows: 
From  the  weight  of  the  combined  sulphates,  etc.,  as  determined 
in  3,  subtract  the  calculated  weights  of  the  calcium  and  mag- 
nesium sulphates,  and  also  the  Fe2O3  and  SiO2.     Consider  the 
remainder  as  Na2SC>4  and  calculate  from  it  the  corresponding 
weight  of  Na2O. 

For  use  in  these  calculations  the  table  on  page  317  is  appended. 

9.  Sulphur    Trioxide. — Slightly  acidify   100  cc.   of  the  water 
with  hydrochloric  acid,  heat  to  boiling  and  slowly  add  an  excess 
of  barium  chloride  solution.     Continue  as  described  in  xv,   i, 
finally  weighing  the  precipitated  BaSO4,  from  which  the  SO3 
may  be  calculated.     BaSO4  X 0.343  =  SO3. 


BOILER    WATER. 


309 


10.  Chlorine. — Measure   TOO  cc.   of  the  water  into  a  clean 
porcelain  dish  or  casserole  and  determine  the  chlorine  volumet- 
rically  by  Mohr's  method,  described  in  xi,  i.     Instead  of  a  N/io 
solution  of  silver  nitrate,  it  is  better  to  prepare  a  solution  con- 
taining 4.7936  grams  of  AgNO3  per  liter,     i  cc.  of  this  solution 
will  equal  o.ooi  gram  of  chlorine. 

11.  By  the  scheme  as  described,  three  portions  of  water  of 
100  cc.  each  have  been  required  in  making  all  the  necessary 
determinations.     Considerable  time  may  be  saved,  with  perhaps 
some  loss  of  accuracy,  by  using  a  separate  portion  for  determin- 
ing the  Fe2O3,  CaO,  and  MgO,  instead  of  waiting  for  the  residue 
obtained  by  evaporation.     The  error  in  this  plan  will  be  mainly 
due  to  the  failure  to  remove  silica,  thus,  possibly,  causing   slight 
increases  in  the  results  for  Fe2O3  and  MgO.      In  most  cases, 
however,  this  error  is  so  trifling  as  to  be  negligible.    When  this 
method  is  adopted  do  not  fail  to  acidify  the  water  at  the  outset 
with  5  cc.  of  strong  hydrochloric  acid,  so  that  the  subsequent 
addition  of  ammonia  will  form  sufficient  ammonium  chloride 
to  prevent  the  precipitation  of  any  calcium  as  carbonate. 

12.  Calculation  of  Results.  —  In   combining  the   acids  and 
bases  only  an  arbitrary  rule  can  be  followed,  and  even  this  is 
subject  to  modification  in  special  cases  according  to  the  judg- 
ment of  the  analyst.     In  general,  proceed  as  follows: 

Combine  the  chlorine  with  sodium.  If  there  is  an  excess 
of  chlorine  combine  it  with  calcium,  then  with  magnesium. 

If  there  is  an  excess  of  sodium,  combine  it  as  Na2O  with  SO3. 
If  the  SO3  is  insufficient  for  all  the  available  Na2O,  calculate 
the  excess  of  the  latter  to  Na2CO3. 

If  SO3  is  in  excess  combine  it  with  CaO  and  then  with 
MgO.  Calculate  any  excess  of  CaO  or  MgO  to  CaCO3  and 
MgC03. 

Calculate   the   Fe2O3  to  FeSO4  if  any  SO3  remains  after 


310  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

satisfying  the  other  bases,  otherwise  to  FeCOa.  It  will  be 
observed  that  the  iron  is  regarded  as  being  in  a  ferrous  con- 
dition. This  is  due  to  the  presence  of  organic  matter  usually. 
If  of  sufficient  importance  the  proper  qualitative  tests  may  be 
made  to  determine  the  condition  of  the  iron. 

The  silica  is  usually  reported  as  SiO2,  although  in  water 
containing  much  sodium  carbonate  it  may  exist  as  sodium 
silicate.  I  have  observed  cases  where  such  a  combination  was 
apparently  necessary  to  satisfy  the  conditions. 

It  will  be  observed  that  the  amount  of  carbon  dioxide  is 
obtained  entirely  by  calculation.  In  the  majority  of  cases  this 
will  suffice,  as  a  fairly  correct  idea  of  the  general  composition 
of  the  dissolved  solids  is  all  that  is  required.  The  presence  of 
a  large  amount  of  calcium  or  magnesium  carbonate  usually 
indicates  the  existence  of  free  carbon  dioxide,  which  probably 
forms  soluble  acid  carbonates  of  the  alkaline  earths. 

13.  In  this  analysis  it  is  sufficiently  accurate  to  regard  milli- 
grams per  liter  as  equivalent  to  parts  per  million.  As  each 
determination  is  made  on  the  basis  of  i/io  of  a  liter,  the  results 
in  milligrams,  multiplied  by  10  will  give  the  parts  per  million. 
Therefore,  after  each  result  is  obtained  in  grams,  record  it  in 
decimilligrams  or  parts  per  million  by  moving  the  decimal  point 
four  places  to  the  right.  When  the  entire  analysis  has  been 
calculated  and  tabulated  in  this  way,  subtract  the  sum  of  the 
constituents,  except  organic  and  volatile  matter,  from  the  total 
solids  and  call  the  difference  organic  and  volatile  matter.  It 
will  usually  be  less  than  the  figure  as  actually  determined  for  the 
jeasons  stated  above. 

Finally,  for  technical  purposes,  it  is  customary  to  report  the 
results  in  grains  per  U.  S.  gallon  of  231  cubic  inches  instead  of 
in  parts  per  million.  The  conversion  is  easily  made  by  means 
of  the  table  on  page  316. 


BOILER  WATER.  311 

14.  Example  of  Calculating  Analysis  of  Boiler-water.  —  Let 

us  suppose  the  various  determinations  have  resulted  as  follows,  in 
parts  per  million: 

Total  solids  .....................  928.0 

Organic  and  volatile  matter  ........  1  79  .o 

Sulphates,  etc  ....................  934-0 

SiO2  ...........................  12.0 

Fe2O3  ..........................  4.0 

CaO  ...........................  165.0 

MgO  ...........................  44.7 

S03  ............................  246.5 

Cl  .............................  60.0 

All  the  constituents  are  shown  except  Na2O,  which  is  deter- 
mined as  follows:  Calculate  the  CaO  and  MgO  to  sulphates 
by  multiplying  by  the  proper  factors  given  in  the  table,  and 
then  add  together  the  following: 


400.4 
MgSO4  ....................    133.4 

Fe2O3  ..............  ....       4.0 

SiO2  ...................     12.  o 

549-8 

Subtract  this  sum,  549.8,  from  the  sum  of  the  sulphates,  etc., 
934.0,  and  consider  the  remainder,  384.2,  as  Na2SO4.  This, 
using  the  table,  is  equivalent  to  167.8  Na2O. 

Now  combine  the  Cl  with  Na.  60  Cl=  99.0  NaCl  (omitting 
more  than  one  decimal  place).  99.0  —  60=  the  Na  required, 
or  39.0.  This  is  equivalent  to  52.5  Na2O.  Subtracting  this 
from  the  original  167.8  Na2O  there  remains  an  excess  of  115.3 
Na2O. 


312  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

Combine  this  with  SO3.  115.3  Na2O=  263.9  Na2S04. 
263.9  —  115.3=148.6,  the  SO3  used.  Subtracting  this  from  the 
total  SOs,  246.5,  there  remains  an  excess  of  97.9  SOs. 

Combine  this  with  CaO.  97.9  SO3  =  166.5  CaS04.  166.5- 
97.9=  68.6,  the  CaO  used.  Subtracting  this  from  the  total 
CaO,  165.0,  there  remains  96.4  CaO  excess. 

Combine  this  with  CO2.     96.4  CaO=  172.0  CaC03. 

Calculate  the  remaining  bases  as  carbonates. 

44.7  MgO=  93-4  MgC03.     4-0  Fe2O3=  5.8  FeC03. 

The  sum  of  the  above  results  in  bold  type,  together  with  the 
Si02, 12,  =812.6.  Subtracting  this  from  the  Total  Solids,  928.0, 
there  remains  115.4  for  the  Organic  and  Volatile  Matter.  It 
will  be  noted  that  this  is  68.6  less  than  the  figure  actually  found 
after  ignition,  indicating  that  some  CO2  was  driven  off  by  the 
heat  employed. 

15.   The  entire  analysis  may  now  be  tabulated  as  follows: 

Parts  per         Grains  per 
Million.  Gallon. 

Sodium  chloride 99  .o  5 . 78 

,     Sodium  sulphate 263.9  15.39 

Calcium  sulphate 166.5  9-71 

Calcium  carbonate 172.0  10 .03 

Magnesium  carbonate 93 .4  5 .45 

Ferrous  carbonate 5.8  o-34 

Silica 12. o  0.70 

Organic  and  volatile  matter H5-4  6.73 


Total  solids 928.0          54. 13 

The  results  in  grains  per  gallon  are  the  ones  usually  reported. 
The  conversion  from  parts  per  million  is  quickly  made  by  means 
of  the  table  on  page  316. 


BOILER   WATER.  313 

16.  Valuation  of  Water  from  Results  of  Analysis.  —  The 
chemist  is  frequently  required  to  give  an  opinion  as  to  the  value 
of  a  water  for  steam  purposes,  basing  his  judgment  on  his  analysis. 
In  this  regard  the  following  points  may  be  considered:  The 
principal  scale-forming  ingredient  is  calcium  sulphate.  Calcium 
and  magnesium  carbonates  also  form  scale  to  a  certain  extent, 
especially  if  much  calcium  sulphate  is  present  to  act  as  a  cement- 
ing agent.  Much  of  the  calcium  and  magnesium  carbonates, 
held  in  solution  by  excess  of  carbon  dioxide  as  acid  carbonates, 
will  tend  to  deposit  as  a  sludge  or  mud  rather  than  as  scale  when 
the  water  is  boiled. 

While  the  other  constituents  ordinarily  found  in  water  are 
not  classed  as  scale-forming,  yet  they  are  practically  all  found 
to  a  greater  or  less  extent  in  the  scale  on  analysis,  showing  that 
with  a  sufficient  cementing  agent  they  all  contribute  to  the  trouble. 

A  large  amount  of  alkali  carbonate  in  water  may  cause  foam- 
ing or  priming  in '  the  boiler,  as  may  also  much  organic  matter. 

Free  acid  is,  of  course,  corrosive  and  is  often  found  in  mine 
waters  owing  to  the  oxidation  of  pyrites. 

Magnesium  chloride  is  regarded  as  an  active  corrosive  agent, 
upon  the  supposition  that  it  is  decomposed  in  the  boiler  with  the 
liberation  of  free  hydrochloric  acid.  When  more  chlorine  is 
present  in  a  water  (containing  magnesium)  than  can  combine 
with  the  sodium  (and  potassium),  magnesium  chloride  is  usually 
considered  present. 


314  TECHNICAL  METHODS  OF  ORE  ANALYSIS 

The  Union  Pacific  Railroad  Company  classifies  the  constituents 
of  boiler  water  as  follows : 

Incrusting,  or  Scale-forming  Solids: 

Oxides  of  Iron  and  Aluminum, 

Calcium  Carbonate, 

Calcium  Sulphate, 

Calcium  Chloride  (corrosive), 

Magnesium  Carbonate, 

Magnesium  Sulphate  (forms  scale  only  in  the  presence  of 

calcium  carbonate), 
Magnesium  Chloride  (corrosive). 

Non-incrusting  Solids: 

Alkali  Carbonates,  Sulphates  and  Chlorides,  and  Organic 

Matter. 
The  quality  of  a  boiler  water  is  judged  as  follows: 

Foaming  and  Priming: 

The  amount  of  non-incrusting  solids  that  a  boiler  water  can 
contain  before  foaming  or  priming  will  take  place  is  about  175 
grains  per  gallon.  The  less  non-incrusting  solids  that  a  given 
water  contains,  the  more  of  the  water  may  be  evaporated  before 
this  degree  of  concentration  will  be  reached. 

The  maximum  limit  permissible  is  generally  taken  as  50  grains 
per  gallon,  although  this  would  be  too  high  unless  the  engine 
occasionally  took  water  very  much  lower  in  non-incrusting  solids. 
For  example,  in  the  case  of  an  average  engine,  of  which  the  boiler 
contains  2000  gallons  and  the  tender  6000  gallons,  after  the  first 
tender  of  water  was  used,  the  non-incrusting  solids  in  the  boiler 
would  have  attained  a  concentration  of  200  grains  per  gallon. 
Therefore,  in  judging  the  foaming  or  priming  qualities  of  a  boiler 


BOILER   WATER.  315 

water,  the  service  that  the  engine  is  performing,  as  well  as  the 
amount  of  non-incrusting  solids  in  solution,  must  be  considered. 

Scale-forming  Matter: 

A  water  containing  less  than  15  grains  per  gallon Good 

"        "  "  "      "     15-20  grains  per  gallon .  .  Fair 

"        "  "  "      "    20-30     "         "       "    ...  Poor 

«        "  "  "      "     30-40     "         "      "...  Bad 

"        «  «  "      "    over  40  "         "      "...  Very  bad 


3i6 


TECHNICAL  METHODS  OF  ORE  ANALYSIS. 


CONVERSION   OF  "MILLIGRAMS  PER  KILOGRAM"  INTO 
"GRAINS  PER  U.    S.  GALLON"  OF  231  CUBIC  INCHES. 


Parts  per 
Million. 

Grains  per 
Gallon. 

Parts  per 
Million. 

Grains  per 
Gallon. 

Parts  per 
Million. 

Grains  per 
Gallon. 

I 

0.0583 

36 

2  .  IOOI 

71 

4.  1418 

2 

o.  1167 

37 

2.1584 

72 

4.2001 

3 

0.1750 

38 

2  .2167 

73 

4.2584 

4 

0.2333 

39 

2.2751 

74 

4.3168 

5 

0.2917 

40 

2-3334 

75 

4-3751 

6 

0.3500 

4i 

2.3917 

76 

4-4334 

7 

o  .  4083 

42 

2.4501 

77 

4.4918 

8 

0.4667 

43 

2  .  5084 

78 

4-5501 

9 

0.5250 

44 

2.5667 

79 

4.6085 

10 

0.5833 

45 

2.6251 

80 

4.6668 

ii 

0.6417 

46 

2.6834 

81 

4-7251 

12 

o  .  7000 

47 

2.7417 

82 

4.7835 

13 

0.7583 

48 

2.  800I 

83 

4.8418 

14 

0.8167 

49 

2  .  8584 

84 

4.9001 

15 

0.8750 

5° 

2.9167 

85 

4.9585 

16 

0-9333 

5i 

2-9751 

86 

5.0168 

i7 

0.9917 

S2 

3-0334 

87 

5-075I 

18 

.0500 

53 

3.0917 

88 

5-J335 

19 

.1084 

54 

3-I50T 

89 

5-1918 

20 

.1667 

55 

3  .  2084 

90 

5-2501 

21 

.2250 

56 

3.2667 

9i 

5-3085 

22 

.2834 

57 

3-3251 

92 

5/3668 

23 

•3417 

58 

3-3834 

93 

5-4251 

24 

.4000 

59 

3.4418 

94 

5-4835 

25 

•4584 

60 

3-5001 

95 

5.54i8 

26 

•5i67 

61 

3.5584 

96 

5.6001 

27 

•5750 

62 

3.6168 

97 

5-6585 

28 

•6334 

63 

3-675i 

98 

5.7i68 

*9 

.6917 

64 

3-7334 

99 

5-7751 

3° 

.7500 

65 

3.79i8 

IOO 

5.8335 

3i 

.8084 

66 

3-8501 

32 

.8667 

67 

3  •  9084 

33 

.9250 

68 

3.9668 

34 

.9834 

69 

4.0251 

35 

2.0417 

70 

4.0834 

One  U.  S.  gallon  of  pure  water  at  60°  F.,  weighed  in  air  at  60°  F.,  at  atmos- 
pheric pressure  of  30  inches  of  mercury,  weighs  58334.9+  grains.  (Mason,  Ex- 
amination of  Water.) 


BOILER   WATER. 


317 


TABLE  OF  FACTORS  FOR  USE  IN  WATER  ANALYSIS. 


Given. 

Required  . 

Factor. 

Log. 

Given. 

Required. 

Factor. 

Log. 

Ca 

CaO 

1.3990 

0.1459 

Na 

NaCl 

2-539° 

o  .  4046 

CaCl2 

CaO 

0-5055 

9.7037 

Na 

Na2CO3 

2.3010 

o  .  3620 

CaO 

CaC03 

I  .  7840 

0.2514 

Na 

Na2O 

1-3470 

o.  1294 

CaO 

CaSO4 

2.4270 

0.3850 

NaCl 

Cl 

0.6059 

9.7824 

CaSO4 

Ca 

0.2945 

9.4691 

NaCl 

Na 

o  .  3940 

9-5954 

Cl 

CaCl2 

1.5660 

0.1947 

NaCl 

Na0O 

0.5308 

9.7249 

Cl 

KC1 

2  .  IO4O 

0.3231 

Na2C03 

Na^SO, 

i  .0640 

o.  1271 

Cl 

NaCl 

I  .  6500 

0.2176 

Na2O 

Na 

0.7423 

9.8706 

Cl 

O 

0.2257 

9-3535 

Na20 

NaCl 

1.8840 

0.2751 

C02 

Na2C03 

2.4IIO 

0.3822 

Na2O 

Na0C03 

1.7080 

0.2326 

Fe,03 

FeC03 

I.I45I 

o.  1615 

Na2O 

Na~SO4 

2  .  2900 

0-3597 

KC1 

K2O 

0.6320 

9.8007 

Na.S04 

Na 

0.3243 

9.5109 

KC1 

K2SO4 

I.  1690 

0.0676 

Na~SO4 

Na2CO3 

o  .  7463 

9.8729 

K2O 

K2C03 

1.4670 

0.1664 

Na,SO4 

Na2O 

0.4368 

9  .  6403 

K2O 
MgC08 

Sf< 

I  .  8490 
0.2888 

0.2669 
9.4606 

SiO, 
SO3" 

C02 
CaSO4 

0.7286 
I  .  7000 

9.8625 
0.2306 

MgO 
MgO 

MgCO, 
MgS04 

2  .  0900 
2  .  9840 

o  .  3202 

0.4747 

S03 
S03 

K2S04 
MgS04 

2.1780 
I  .  5040 

o  •  3380 
0.1773 

Mn3O>4 

MnCO3 

1.5070 

o  .  i  780 

sos 

Na2S04 

1.7760 

0.2494 

CHAPTER  XXXIII. 

COAL   AND    COKE. 

1.  The    proximate   analysis    of    coal    and    coke  comprises 
determinations  for  MOISTURE,  VOLATILE  COMBUSTIBLE  MATTER, 
FIXED  CARBON  and  ASH.     SULPHUR  and  PHOSPHORUS  are  some- 
times required  in  addition. 

The  results  obtained  for  moisture,  volatile  combustible  matter 
and  fixed  carbon  depend  to  a  considerable  extent  upon  the  par- 
ticular plan  of  working  adopted  by  the  operator.  While  the  usual 
methods  are  more  or  less  conventional  and  arbitrary,  there  is 
as  yet  no  uniform  agreement  as  to  details.  The  methods  given 
below  are  those  adopted  in  the  report  of  the  committee  on  coal 
analysis  of  the  American  Chemical  Society.* 

2.  Preparation  of  the  Sample. — As  soon  as  the  coal  or  coke 
is  received  crush  it  sufficiently  and  quarter  it  down  to  about 
100  grams.     Grind  this  coarsely,  about  as  fine  as  is  possible  with 
an   ordinary  coffee-mill.     Transfer  a  portion  of  this  sample  at 
once  to  a  tightly  stoppered  bottle  for  use  in  determining  moisture. 

Grind  12  to  1 5  grams  of  the  remainder  moderately  fine  and 
transfer  to  a  tightly  stoppered  bottle  for  use  in  determinations 
other  than  moisture. 

3.  Moisture.  —  Dry    i    gram    of    the   coal,   uncovered,  in   a 
weighed  porcelain  or  platinum  crucible  at  104°-!  07°  C.  for  one 

*  Jour.  Am.  Chem.  Soc.,  XXI,  1116. 


COAL  AND  COKE.  319 

hour,  best  in  a  double-walled  bath  containing  pure  toluene. 
Cool  in  a  desiccator  and  weigh  covered.  Loss  of  toluene  may 
be  prevented  by  attaching  a  reflux  condenser  to  the  steam  vent 
of  the  bath. 

With  coals  high  in  moisture  and  in  all  cases  where  accuracy 
is  desired,  determinations  must  be  made  both  with  the  coarsely 
ground  and  with  the  powdered  coal.  When,  as  will  usually  be 
the  case,  more  moisture  is  found  in  the  coarsely  ground  than 
in  the  powdered  coal,  a  correction  must  be  applied  to  all  deter- 
minations made  with  the  latter.  The  correction  factor  may  be 
found  as  follows :  Divide  the  difference  in  moisture  by  the  per  cent, 
of  other  constituents  than  moisture,  as  found  in  the  powdered 
coal.  Multiply  the  per  cent,  of  each  constituent  as  found  in  the 
powdered  coal  by  the  quotient,  and  subtract  the  resulting  product 
from  the  amount  of  the  given  constituent. 

Thus,  suppose  the  results  of  an  analysis  give: 

Coarsely  Ground     Powdered 
Coal.  Coal. 

Moisture 12.07  10.39 

Volatile  combustible  matter 34 . 2  5 

then  the  correction  factor  will  be 

12.07  —  10.39       1.68 

— —  =  -5— 7-=  0.0187 
100  —  10.39       89.61 

and  the  true  per  cent,  of  volatile  combustible  matter  will  be 
34.25  -(34-25  X 0.0187)=  33.61. 

4.  Volatile  Combustible  Matter. — Place  i  gram  of  the  fresh, 
undried,  powdered  coal  in  a  20-  or  3o-gram  weighed  platinum 
crucible  having  a  tightly  fitting  cover.  Heat  over  the  full 


320  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

flame  of  a  Bunsen  burner  for  seven  minutes.  The  crucible 
should  be  supported  on  a  platinum  or  pipe-stem  triangle  with 
the  bottom  6  to  8  cm.  above  the  top  of  the  burner.  The  flame 
should  be  fully  20  cm.  high  when  burning  free,  and  the  deter- 
mination should  be  made  in  a  place  free  from  draughts.  The 
upper  surface  of  the  cover  should  burn  clear,  but  the  under  sur- 
face should  remain  covered  with  carbon.  To  find  "volatile 
combustible  matter"  subtract  the  per  cent,  of  moisture  from  the 
loss  found  here. 

The  term  "Volatile  Combustible  Matter"  does  not  represent 
any  definite  compound  or  class  of  compounds  which  exist  in 
the  coal  before  heating.  The  method  is  arbitrary  and  the  appli- 
cation of  higher  temperatures  will  expel  more  volatile  matter. 

(Note. — I  have  found  western  lignites  to  suffer  a  serious 
mechanical  loss  when  subjected  at  once  to  the  full  heat  of  a 
Bunsen  burner  as  directed  above,  the  loss  sometimes  amount- 
ing to  several  per  cent.  To  avoid  this,  with  such  coals,  I  proceed 
as  follows:  Heat  the  covered  crucible  over  a  Bunsen  burner 
with  the  flame  turned  very  low  and  not  touching  the  crucible. 
After  heating  for  several  minutes  in  this  manner,  increase  the 
temperature  very  gradually  and  only  as  fast  as  the  coal  will 
permit  without  suffering  mechanical  loss.  Finally,  when  the 
full  power  of  the  Bunsen  flame  is  attained  adjust  it  as  directed 
above  and  continue  the  heating  for  five  minutes.  Cool  in  desic- 
cator and  weigh  as  usual.) 

5.  Ash. — Burn  the  portion  of  powdered  coal  used  for  the 
determination  of  moisture,  at  first  over  a  very  low  flame,  with 
the  crucible  open  and  inclined,  till  free  from  carbon.  If  properly 
treated  this  sample  can  be  burned  much  more  quickly  than  the 
dense  carbon  left  from  the  determination  of  volatile  matter. 
It  is  advisable  to  examine  the  ash  for  unburned  carbon  by  moisten- 
ing it  with  alcohol. 


COAL  AND  COKE. 


321 


When  the  sulphur  in  the  coal  is  in  the  form  of  pyrites,  that 
compound  is  converted  almost  entirely  into  ferric  oxide  in  the 
determination  of  ash,  and,  since  three  atoms  of  oxygen  replace 
four  atoms  of  sulphur,  the  weight  of  the  ash  is  less  than  the  weight 
of  the  mineral  matter  in  the  coal  by  five-eighths  of  the  weight 
of  the  sulphur.  While  the  error  from  this  source  is  sometimes 
considerable,  the  committee  does  not  recommend  such  a  correc- 
tion for  "proximate"  analyses.  When  analyses  are  to  be  used 
as  a  basis  for  calculating  the  heating  effect  of  the  coal  a  correc- 
tion should  be  made. 

6.  Fixed  Carbon. — This  is  found  by  subtracting  the  per  cent, 
of  ash  from  the  per  cent,  of  coke  or  residue  left  after  expelling 
the  volatile  matter.     Or,  it  is  the  difference  between  the  sum  of 
the    other    constituents    determined    and    100.     Sulphur,    which 
passes  partly  into  the  "volatile  combustible  matter"  and  partly 
into  the  coke,  is  not  considered  in  the  calculation. 

7.  Coking   Quality.  —  (Not  included  in  committee's  report). 
The  condition  of  the  residue  left  in  the  crucible  after  expelling 
the  volatile  matter  is  a  good  indication  of  the  coking  qualities  of 
a  coal,  and  the  latter  may  usually  be  reported  as  "coking"  or 
"non-coking"  accordingly.     A  better  test,  however,  is  to  place 
a  quantity  of  the  coal  in  the  shape  of  small  fragments  in  a  clay 
crucible,  cover  the  latter  and  expose  to  a  strong  heat  in  a  muffle. 
Be  careful  not  to  fill  the  crucible  too  full  or  the  mass  may  swell 
up  and  displace  the  cover.    When  all  volatile  matter  has  appar- 
ently been  expelled  and  the  crucible  is  at  a  bright  red  heat,  remove 
from  the  mufBe  and  allow  to  cool  with  the  cover  on.     When 
cold,  examine  the  residue,  and  from  its  fused  or  unfused  con- 
dition, its  porosity  or  density,  etc.,  decide  as  to  the  quality  of 
the  coke.     Of  course  this  test  is  unnecessary  with  coals,  such 
as  lignites,  that  give  only  a  loose  non-coherent  residue  in  the 
platinum  crucible  after  expelling  the  volatile  matter. 


322  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

8.  Sulphur. — This  is  determined  by  Eschka's  method  as 
follows:  Weigh  i  gram  of  the  finely  powdered  coal  into  a  platinum 
dish  of  75-  to  loo-cc.  capacity.  Add  1.5  grams  of  an  intimate 
mixture  of  i  part  dry  sodium  carbonate  and  2  parts  magnesium 
oxide.  The  magnesium  oxide  should  be  of  a  light  and  porous 
nature,  not  compact  and  heavy.  Mix  the  coal  and  other  con- 
stituents in  the  dish  very  thoroughly  with  a  platinum  spatula 
or  glass  rod.  Now,  holding  the  Bunsen  burner  in  the  hand  at 
first,  heat  the  dish  very  cautiously  and  raise  the  temperature  very 
slowly,  especially  with  soft  coals.  When  the  strong  glowing  has 
ceased,  increase  the  heat  gradually,  placing  the  burner  under 
the  dish,  until  in  about  fifteen  minutes  the  bottom  of  the  dish 
is  at  a  low  red  heat.* 

Stir  the  mixture  occasionally  with  a  platinum  rod  and  when 
the  carbon  is  completely  burned  allow  to  cool  and  transfer  the 
residue  to  a  beaker.  Rinse  out  the  dish  into  the  beaker  with 
about  50  cc.  of  water,  add  15  cc.  of  saturated  bromine  water 
and  boil  the  mixture  for  five  minutes.  Remove  from  the  heat, 
allow  the  insoluble  matter  to  settle  and  decant  the  solution  through 
a  filter.  Treat  the  residue  twice  with  30  cc.  of  water,  bringing 
it  to  a  boil  each  time,  allowing  to  settle  and  decanting  through 
the  filter.  Finally,  transfer  the  residue  to  the  filter  and  wash 
until  the  filtrate  gives  only  a  slight  opalescence  with  nitric  acid 
and  silver  nitrate.  Add  to  the  filtrate,  which  should  have  a 
volume  of  about  200  cc.,  1.5  cc.  of  strong  hydrochloric  acid  and 
boil  the  solution  until  the  bromine  is  expelled.  Now  add  to 
the  boiling  liquid  10  cc.  of  a  10  per  cent,  solution  of  barium 
chloride.  This  should  be  added  drop  by  drop,  especially  at 
first,  with  constant  stirring.  Allow  to  stand  on  a  hot  plate  or 
over  a  low  flame  until  the  solution  is  perfectly  clear,  and  then 

*  To  avoid  possible  absorption  of  sulphur  from  the  illuminating  gas  it  is  ad- 
visable to  place  the  dish  in  a  hole  cut  in  a  piece  of  asbestos  board. 


COAL   AND   COKE.  323 

filter  off  the  barium  sulphate,  washing  with  hot  water  until  free 
from  chlorides.  Transfer  the  filter  and  moist  precipitate  to  a 
weighed  platinum  crucible  and  heat  with  a  low  flame  until  the 
paper  is  burned.  Finally  heat  to  redness,  cool  in  a  desiccator 
and  weigh  the  BaSC>4.  The  weight  of  the  latter,  multiplied  by 
°-I373>  will  giye  the  weight  of  the  sulphur,  from  which  the  per- 
centage may  be  calculated. 

To  insure  accuracy  a  blank  determination  should  be  made, 
using  all  the  reagents  in  the  same  quantities  and  carrying  out 
the  entire  process  in  exactly  the  same  manner  as  with  the  coal. 
Subtract  the  weight  of  any  barium  sulphate  found  from  that 
obtained  in  the  coal  test  and  calculate  the  true  percentage  of 
sulphur  in  the  coal  from  the  remainder. 

If  the  coal  contains  much  pyrite  or  calcium  sulphate,  some 
sulphur  may  still  remain  with  the  residue  of  magnesium  oxide 
and  ash.  Dissolve  this  residue  in  hydrochloric  acid  in  slight  excess, 
dilute  sufficiently,  heat  to  boiling  and  precipitate  as  above  with 
barium  chloride.  Filter  off  any  barium  sulphate  obtained,  ignite, 
and  weigh  as  before,  and  add  the  weight  to  that  of  the  main  por- 
tion. The  experiments  of  Geo.  Steiger,  under  the  direction 
of  Dr.  Hillebrand,  demonstrate  the  necessity  of  always  examin- 
ing this  residue;  9  samples  of  coal  showing  from  0.032  to  0.114 
per  cent,  additional  sulphur,  where  the  total  sulphur  ran  from 
0.625  to  4.561  per  cent. 

9.  Error  in  Determining  Volatile  Combustible  Matter. — 
Mead  and  Attix  *  call  attention  to  the  fact  that  while  the  above 
described  method  of  heating  over  a  Bunsen  burner  may  be  suf- 
ficient for  soft  coals  it  is  quite  inadequate  for  coke  or  anthracite 
which  require  the  heat  of  a  blast-lamp  to  drive  off  all  the  volatile 
combustible  matter.  They  further  show  that  during  this  heating 

*  Jour.  Am.  Chem.  Soc.,  XXI,  1137. 


324  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

there  is  a  considerable  loss  by  oxidation.  With  coke  and 
anthracite  they  therefore  proceed  as  follows:  Heat  in  an  atmos- 
phere of  nitrogen,  using  a  Shimer  crucible,*  first  over  a  Bunsen 
burner  for  several  minutes  and  then  over  a  blast  for  fifteen 
minutes.  As  an  alternative  method,  giving  nearly  the  same 
results,  omit  the  atmosphere  of  nitrogen  but  make  two  similar 
heatings  and  weighings,  using  an  ordinary  covered  platinum' 
crucible.  The  loss  in  a  series  of  several  consecutive  heatings 
after  the  first  is  shown  to  be  practically  a  constant,  and  is  due 
entirely  to  oxidation.  Therefore,  deduct  the  loss  sustained  in  the 
second  heating  from  the  loss  in  the  first  to  obtain  the  loss  due 
only  to  volatile  combustible  matter. 

This  method  is  undoubtedly  much  more  satisfactory  for  coke 
and  anthracite  than  the  one  given  above,  but  as  the  results  in 
any  case  are  intended  to  be  only  comparative,  it  is  perhaps  not 
advisable  to  adopt  it  for  ordinary  work  until  there  is  some  general 
agreement  in  the  matter. 

10.  Phosphorus.  —  Weigh  5  grams  of  the  coarsely  crushed 
coal  or  coke  (2)  into  a  platinum  dish  and  burn  completely  to 
ash,  best  in  a  muffle.  Transfer  the  residue  to  a  beaker  and  digest 
with  hydrochloric  acid  for  some  time  to  dissolve  the  phosphorus 
compounds,  then  filter  into  an  8-oz.  beaker,  washing  with  water, 
and  evaporate  the  filtrate  to  dryness  on  a  sand-bath  or  hot  plate. 
Add  to  the  residue  in  the  beaker  25  cc.  of  strong  nitric  acid,  cover 
the  beaker  and  boil  to  about  12  cc.  Now  dilute  with  12  cc.  of 
water  and  filter,  washing  with  water.  Receive  the  filtrate  in  a 
6-oz.  flask.  The  total  volume  should  not  exceed  50  cc.  Heat  to 
4o°-45°  C.,  add  60  cc.  of  molybdate  solution  (see  xxn,  7),  previously 
filtered  and  heated  to  4o°-45°  C.,  stopper  the  flask  and  shake 
for  five  minutes.  Allow  to  stand  in  a  warm  place  for  fifteen 

*  Jour.  Am.  Chem.  Soc.,  XXI,  557. 


COAL  AND   COKE.  325 

minutes  and  then  filter  through  a  y-cm.  washed  filter  (Baker  and 
Adamson,  A  grade)  that  has  been  previously  dried  at  no°C. 
and  weighed.  Wash  with  a  2  per  cent,  nitric  acid  solution  till 
free  from  salts,  and  then  twice  with  95  per  cent,  alcohol.  Dry 
twenty  minutes  at  no°C.  and  weigh.  The  dried  residue  con- 
tains 1.63  per  cent,  of  phosphorus,  therefore  multiply  the  weight 
found  by  0.0163  to  obtain  the  weight  of  phosphorus  in  the  amount 
of  coal  taken. 

Always  test  the  filtrate  with  more  molybdate  solution,  omitting 
the  washings. 

ii.  Specific  Gravity. — In  the  matter  of  specific  gravity  either 
one  of  two  things  may  be  required : 

i.  The  true  specific  gravity,  or  specific  gravity  of  the  particles. 
.  2.  The  apparent  specific  gravity,  or  specific  gravity  of  the 
mass  taken  as  a  whole. 

Proceed  as  follows: 

Select  a  lump  of  convenient  size,  weighing,  perhaps,  from  10 
to  20  grams,  and  weigh  it.  Call  this  weight  a. 

Place  the  piece  in  distilled  water  under  a  bell-jar  and  exhaust 
the  air  from  the  latter.  Admit  the  air,  carefully  wipe  off  the 
surface  of  the  coal,  now  saturated  with  water,  and  weigh  again. 

Call  the  increase  in  weight,  or  weight  of  the  absorbed  water,  b. 

Now  suspend  the  wet  coal  by  means  of  a  fine  horse -hair  and 
weigh  it  immersed  in  water.  Call  this  weight  c. 

Then, 

a 

=  true  specific  gravity, 

d — c 

and 

a 
a  —  (c-.b\=  aPParent  specific  gravity. 


326  TECHNICAL  METHODS  OF   ORE  ANALYSIS. 

12.  Heating  Value  of  Coal. — The  heating  value  of  a  coal  is 
usually  expressed  either  in  terms  of  British  Thermal  Units 
(abbreviated,  B.T.U.),  or  in  Calories  (abbreviated  to  Cal.). 

The  British  Thermal  Unit  is  the  heat  required  to  raise  the 
temperature  of  i  pound  of  pure  water,  at  or  near  its  temperature 
of  maximum  density,  39.1  F.,  through  i  degree  Fahrenheit. 

The  Calorie  is  the  heat  necessary  to  raise  the  temperature  of  I 
kilogram  of  water  from  4°  C.  to  5°  C. 

i  B.T.U.  is  equivalent  to  0.252  Calorie. 

i  Calorie  is  equivalent  to  3.968  B.  T.  U. 

To  reduce  B.T.U.  per  pound  to  Calories  per  kilogram,  mul- 
tiply by  5/9. 

To  reduce  Calories  per  kilogram  to  B.T.U.  per  pound,  multiply 

by  9/5- 

The  heating  value  of  a  coal  is  most  accurately  determined  by 
means  of  a  coal  calorimeter,  and  a  fairly  correct  result  may  be 
obtained  by  calculation  from  an  ultimate  analysis.  Descrip- 
tions of  both  these  methods  may  be  found  by  consulting  the 
standard  authorities,  but  are  omitted  here  as  beyond  the  present 
scope  of  this  treatise.*  Attempts  have  been  made  to  calculate 
the  heating  value  of  a  coal  from  the  results  of  its  proximate  anal- 
ysis, and  the  following  formulas  are  given  as  sufficiently  accurate 
for  rough  heat  calculations. 

13.  Formula  of  F.  Haas  (West  Virginia  Geol.  Survey). 
B.T.U.  per  pound  =  156.75   (100  —  %  ash  —  %  sulphur  — 

%  moisture)  +  (40.50  X  %  sulphur). 

Calories  per  kilogram  =  87.1  (100  —  %  ash  —  %  sulphur  — 
%  moisture)  -f-  (25-5°  X  %  sulphur). 

14.  Goutal's  Formula.f 

82 C  +  aV  =  Calories  per  kilogram. 

*  See  Chemical  Engineer,  Vol.  I,  pp.  1-98,  for  a  clearly  written  article, 
f  Jour.  f.  Gasbeleuchtung  u.  Wasserorgung,  XL VIII,   1006. 


COAL  AND  COKE. 


327 


C  =  Fixed  Carbon,  V  =  Volatile  Constituents,  a  is  a  variable 
factor  dependent  upon  the  Volatile  Constituents,  Vi,  of  the  pure 
(water-and  ash-free)  coal. 

V  X  100 


V,  = 


C  +   V 


15.    The  following  table  gives  the  values  of  a  corresponding 
to  values  of  Vi  from  i  to  40. 


v, 

a 

V, 

a 

V, 

a 

V, 

a 

v, 

a 

v, 

a 

V, 

a 

i-5 

!S° 

10 

130 

16 

"5 

21 

108 

26 

102 

3i 

97 

36 

9i 

5 

i45 

II 

127 

17 

113 

22 

107 

27 

101 

32 

97 

37 

88 

6 

142 

12 

124 

18 

112 

23 

i°5 

28 

100 

33 

96 

38 

85 

7 

i39 

13  ' 

122 

19 

110 

24 

104 

29 

99 

34 

95 

39 

82 

8 

136 

14 

120 

20 

I09 

25 

103 

3° 

98 

35 

94 

40 

80 

9 

i33 

•15 

II7 

1 6.  As  an  example  of  how  the  results  obtained  by  the  above 
formulas  compare  with  that  of  the  bomb  calorimeter,  the  fol- 
lowing instance  is  given: 

Proximate  Analysis  of  Coal. 


Moisture, 
Volatile, 
Fixed  Carbon, 
Ash, 

Sulphur, 

1.460 
10.880 

8i.535 
6.125 

100.000 

0.807 

Calories  per  kilogram  determined  by  calorimeter,  7778. 
By  Haas's  formula: 

87.1  (100  —  6.125  —  0.807  —  1.46)  +  (22.5  X  0.807)  —  7909 
Cal.  per  kilo. 


328  TECHNICAL  METHODS  OF  ORE  ANALYSIS. 

By  GoutaPs  formula: 

,  10.88  X  100 


From  the  table  we  find  that  with  Vi  equal  to  11.78,  a  =  124.7 
Then, 

82  (81.535)  +  124-7  (10.88)  =  8068  Cal.  per  kilo. 


CHAPTER  XXXIV. 

TESTING  CRUDE  PETROLEUM. 

OWING  to  frequent  discoveries  of  petroleum  in  new  districts 
the  western  technical  chemist  is  liable  to  be  required  to  test  and 
compare  samples  with  a  view  of  determining  their  commercial 
value.  The  following  tests  will  usually  suffice: 

1.  Preliminary  Note. -^  The  sample    as   received  is  likely  to 
contain  water,  either  from  the  original  flow  being  mixed  with 
water,  or  from  the  containing  vessel  having  been  rinsed  out  with 
water  and  not  subsequently  dried.     Therefore,  allow  the  sample 
to  stand  for  some  time  and  settle  out  as  much  as  possible  before 
beginning  the  tests. 

2.  Specific  Gravity. — This  may  be  taken  with  the  hydrom- 
eter if  there  is  a  sufficient  quantity  of  the  oil  at  hand.     Fill  the 
hydrometer  jar  about  four-fifths  full  and  introduce  the  hydrometer 
carefully  so  as  not  to  smear  the  stem  with  oil  above  the  point 
to  which  it  would  naturally  sink.     The  hydrometer  to  employ 
is    the    "Standard    Baume    Hydrometer   for    Coal    Oil."     Hold 
a  piece  of  white  paper  back  of  the  jar  and  note  the  point  where 
the  lower  portion  of  the  meniscus  touches  the  scale.    Take  also  the 
temperature  of  the  oil  and  subtract  i°  Baume'  from  the  hydrom- 
eter reading  for  every  increase  of  10°  Fahr.,  or  5.5°  C.,  above 
60°  Fahr.,  or  15.5°  C.     The  specific  gravity  may  be  found  by 

329 


330  TECHNICAL   METHODS  OF  ORE  ANALYSIS. 

comparing    the   hydrometer  reading   with  a  table   (see  p.  341), 

or  by  the  formula  •    I44'3P0.     "B°"  is  the  reading  Baume*. 
-3  +  -b 


If  the  quantity  of  oil  is  too  small  for  filling  a  hydrometer  jar 
the  specific  gravity  may  be  taken  with  a  10-  or  25-cc.  picnometer. 
The  picnometer  should  be  tested  with  water  at  15.5°  C.  and  then 
with  the  oil  at  the  same  temperature.  The  weight  of  the  oil 
divided  by  the  weight  of  the  same  volume  of  water,  both  at 
15.5°  C.,  will  give  the  specific  gravity  at  this  temperature. 

3.  Distillation  Test,  Engler's  Method.  —  Arrange  a  fractional 
distillation-flask  with  a  side  tube  and  Liebig  condenser  as  in 
the  figure.  The  apparatus  should  be  approximately  of  the 
dimensions  shown.  If  possible,  have  the  side  tube  long  enough 
to  permit  of  bending  the  outer  end  downward  so  as  to  fit  into 
the  vertical  condenser.  When  this  cannot  be  done  without 
bringing  the  condenser  and  receiver  too  near  the  flame,  use  a 
properly  bent  glass  tube  as  an  extension.  The  joints  may  be 
cork,  or  strips  of  cotton  cloth  moistened  with  glycerine  wrapped 
around  and  wound  tightly  with  small  string.  Rubber  will  not 
answer  so  well,  as  it  is  acted  upon  by  the  hot  vapors  and  may 
swell  up  or  split.  A  Bunsen  burner  or  alcohol  lamp  may  be 
used  for  heating.  A  piece  of  wire  gauze  may  be  placed  under 
the  flask  at  first  and  afterward  removed  and  the  naked  flame 
employed  as  a  higher  temperature  is  required.  The  flame 
should  be  screened  to  protect  it  from  draughts. 

4.  By  means  of  a  graduated  pipette,  place  100  cc.  of  the 
oil  in  the  flask  and  then  arrange  a  thermometer,  graduated  to 
400°  C.,  inserted  through  a  cork  in  the  top  of  the  flask,  so  that 
the  top  of  the  bulb  is  about  opposite  the  junction  of  the  side 
tube  and  neck  of  the  flask.  Heat  the  oil  so  that  it  distils  as  nearly 
as  possible  at  the  rate  of  2  to  2.5  cc.  per  minute.  As  the  tem- 
perature rises  above  100°  C.  be  watchful  for  water  in  the  oil. 
Water  is  apt  to  cause  sudden  violent  bumps  when  it  collects 


TESTING  CRUDE  PETROLEUM. 


331 


under  the  oil.     It  also  evaporates  and  a  portion  condenses  in  a 
drop  on  the  thermometer  bulb.    When  this  drop  falls  back  into 


FIG.  21. 


the  hot  oil  it  is  liable  to  cause  a  small  explosion  and  perhaps 
spoil  the  analysis.  It  is  best  to  heat  very  cautiously  at  first,  and 
if  water  appears  on  the  bulb  remove  the  thermometer  and  absorb 
it  with  filter-paper.*  Oils  with  but  little  naphtha  are  apt  to  give 
the  most  trouble  in  this  respect,  as  they  may  become  very  hot 

*  A  safer  plan  is  to  lower  the  thermometer  so  the  bulb  is  immersed  in  the  Hquid, 
until  a  temperature  of,  say,  120°  C.  is  attained,  occasionally  agitating  the  flask 
until  all  water  is  expelled.  Then  raise  the  thermometer  to  its  proper  place  and 
proceed  as  described. 


332 


TECHNICAL  METHODS  OF  ORE  ANALYSIS. 


and  dangerous  before  the  thermometer  in  the  neck  shows  much 
rise,  and  if  a  drop  of  water  then  falls  back  a  violent  burst  of  steam 
is  the  result.  Continue  the  heating  until  the  thermometer 
indicates  a  temperature  of  i5o°C.  Collect  the  distillate  in  a  50- 
cc.  cylindrical  graduate.  When  a  temperature  of  1 50°  is  reached, 
remove  the  lamp  a  moment  so  that  the  temperature  will  drop  back 
20°,  then  replace  it  and  again  heat  to  150°.  Repeat  these  opera- 
tions until  no  appreciable  additional  distillate  is  thus  obtained. 
Read  the  number  of  cubic  centimeters  in  the  graduate,  quickly 
pour  off  the  oil  and  replace  the  graduate  again.  Now  increase 
the  heat  so  that  the  thermometer  gradually  rises  to  200°  and 
then  repeat  the  cooling  and  heating  as  before.*  Measure  the 
fraction  thus  obtained  and  then  increase  the  heat  similarly  to 
250°  and  300°,  and  then  above  300°,  until  nothing  but  coke 
remains  in  the  flask.  The  distillate  up  to  150°  is  called  naphtha. 
The  next  three  portions  are  illuminating  oils,  the  fraction? 
obtained  showing  the  proportions  of  the  different  grades.  The 
distillate  coming  off  above  300°  is  called  lubricating  oil,  and 
what  is  finally  left  in  the  flask  constitutes  the  residuum  and  coke, 
The  distillation  is  usually  carried  as  far  as  possible. 


EXAMPLE  SHOWING  TABULATION  OF  RESULTS. 
Specific  gravity  of  the  crude  oil  at  60°  Fahr.,  0.841. 


Temperature  of  Distillation. 

Per  Cent,  of  Product. 

Nature  of  Product. 

Below  150°  C        

*8.S 
I2'5l  Total 

£SJ**- 

2.0 

3-o 

Naphtha. 
\    Illuminating-oils. 

Lubricating  -oil. 
Coke. 

From  i  "}O°  to  200°  

"         200°   "    2500    

"         2<0°   "    3OO°.  .. 

100.  0 

*  I  have  found  it  best,  at  this  point,  to  drain  the  water  from  the  condenserf 
so  as  to  prevent  subsequent  products  from  thickening  or  solidifying  in  the  tube. 


MISCELLANEOUS. 

Determination  of  Antimony  and  Tin  in  Babbitt,  Type  Metal, 
and  Other  Alloys.* — The  following  process,  found  generally  applic- 
able to  alloys  and  to  the  sulphides  of  antimony  and  tin,  either  in 
the  solid  state  or  in  proper  solution,  claims  nothing  in  particular 
as  original,  except  the  direct  determination  of  the  antimony  and  tin 
in  one  portion  of  the  alloy  without  separating  the  other  ingredients, 
and  the  titration  of  antimony  and  tin  when  both  are  present  in 
solution.  The  direct  titration  in  an  alloy  without  separation  in  the 
other  ingredients  may  not  be  applicable  in  all  cases,  but  it  is  in  most 
cases,  and  where  it  is  not  the  sulphide  separation  mentioned  below 
is  made  use  of  and  the  sulphides  treated  in  almost  the  same  way 
as  the  original  alloy.  If  other  metals,  besides  tin  and  antimony, 
are  to  be  determined,  Rossing's  method  given  below  gives  a  good, 
quick  separation,  but  the  antimony  and  tin  are  determined  by 
direct  titration,  if  possible,  in  another  portion  of  the  alloy. 

Where  only  antimony  and  tin  are  sought,  the  alloy  may  be 
decomposed  by  nitric  acid,  by  sulphuric  acid,  or  by  a  mixture  of 
sulphuric  acid  and  potassium  sulphate.  Where  possible,  sul- 
phuric acid  alone  is  used.  If  nitric  acid  is  first  used,  it  must 
subsequently  be  expelled  by  boiling  with  sulphuric  acid,  and 
after  the  nitric  acid  is  expelled,  some  tartaric  acid  and  some 
potassium  sulphate  must  be  added,  and  the  melt  heated  till  all 
carbon  has  been  oxidized.  This  leaves  the  antimony  and  tin  in 
the  proper  state  for  the  titrations. 

The  two  standard  solutions  required  are  an  N/io  potassium 
permanganate,  and  an  N/io  iodine  solution.  For  antimony 
determination,  the  permanganate  solution  should  be  standard- 
ized by  C.P.  antimony  or  tartar  emetic  (anhydrous)  of  the  proper 

*  Method  of  W.  H.  Low,  Jour.  Am.  Chem.  Soc.,  XXIX,  66. 

333 


334  TECHNICAL   METHODS  OF   ORE  ANALYSIS. 

composition.  If  properly  done,  these  standards  will  agree  and 
both  will  agree  with  a  standardization  made  with  oxalic  acid  in 
the  regular  way,  but  always  standardize  with  antimony  or  its 
compounds  by  heating  with  sulphuric  acid,  diluting  and  adding 
the  same  amount  of  hydrochloric  acid  as  is  used  with  the  alloy. 
In  this  way  correct  results  are  insured.  The  iodine  solution  is 
compared  with  a  solution  of  sodium  thiosulphate  of  known  value. 

From  0.5  gram  to  i  gram  of  the  finely  divided  alloy  is  taken, 
and  as  the  method  is  generally  the  same,  the  standardization  of 
the  permanganate  will  be  described  together  with  the  subsequent 
titration  of  the  tin. 

0.1202  gram  of  finely  powdered  C.P.  antimony  (=  0.3234 
gram  tartar  emetic)  and  o.  1190  gram  of  tin  are  placed  in  a  450  cc. 
Jena  glass  Erlenmeyer  flask  and  about  10  cc.  of  strong  sulphuric 
acid  (free  from  chlorine  compounds)  added;  3-4  grams  of  potas- 
sium sulphate  are  sometimes  used  and  can  be  added  here.  Heat 
till  the  metals  are  all  in  solution  (or  the  alloy  thoroughly  decom- 
posed) and  all  separated  sulphur  has  been  boiled  out  of  the  flask. 
All  sulphurous  acid  will  also  be  expelled  by  this  time.  Do  not 
drive  off  all  free  sulphuric  acid,  but  have  enough  left  to  keep  the 
melt  from  getting  hard  on  cooling.  About  7-10  cc.  left  is  enough. 
These  operations  take  only  a  few  minutes.  Cool  and  add  50  cc. 
of  water  and  10  cc.  of  strong  hydrochloric  acid  and  heat  to  get  all 
possible  in  solution.  Large  quantities  of  lead  sulphate,  even, 
will  dissolve,  and  the  solution  will  become  clear.  However,  the 
object  is  to  get  the  antimony  and  tin  in  solution,  and  this  is  all 
that  is  necessary.  With  the  quantity  of  antimony  taken  no 
tartaric  acid  is  necessary,  but  with  larger  quantities  a  few  grams 
of  tartaric  acid  must  be  added.  Tartaric  acid  has  no  effect  on 
either  titration.  Some  stannic  compound  with  sulphuric  acid 
may  go  into  solution  with  some  difficulty,  but  no  attention  need 
be  paid  to  it  here,  as  it  will  dissolve  when  we  get  through  with 


M ISC ELL  A  NEO  US.  335 

s;he  antimony,  if  not  before.  Cool  the  solution  and  add  about 
no  cc.  more  of  water  and  25-30  cc.  (with  small  amounts  of  Sb, 
such  as  is  in  solder,  a  total  of  20  cc.  strong  HC1  in  total  volume  of 
200  cc.  appears  enough)  more  of  strong  hydrochloric  acid. 
Thoroughly  cool  this  mixture  and  proceed  to  titrate  with  per- 
manganate. Add  the  latter  till  the  last  drop  colors  the  whole 
solution  pink.  The  end  point  is  sharp,  but  the  color  may  not 
remain  long,  owing  to  the  large  quantity  of  hydrochloric  acid 
present.  If  less  hydrochloric  acid  were  present,  say  10  cc.  in 
the  total  volume  of  200  cc.,  the  end  point  would  be  sharp,  but 
would  apparently  occur  at  about  19.60-19.70  cc.,  instead  of 
20.00  cc.,  as  it  should.  The  true  end  point  under  these  circum- 
stances is  troublesome  to  find.  But  even  an  incorrect  end  point 
may  give  good  results,  if  the  solution  has  been  standardized  in 
exactly  the  same  way.  The  determination  of  the  antimony  or 
standardization  of  the  permanganate  is  now  finished  and  the  tin 
is  the  next  consideration.  The  titrated  solution  contains  anti- 
monic  chloride  and  stannic  chloride,  besides  other  things  of  no 
particular  moment.  Pour  this  solution  into  a  500  cc.  round- 
bottomed  flask  and  rinse  out  the  Erlenmeyer  flask  with  about 
50  cc.  of  strong  hydrochloric  acid  and  add  washings  to  main 
solution.  The  main  solution  should  be  at  least  one-fifth  by 
volume  of  strong  hydrochloric  acid  (the  regular  strong  C.P.  acid). 
Add  about  i  gram  of  finely  powdered  C.P.  antimony  *  and  place 
on  the  steam  bath  for  about  15  minutes,  shaking  once  in  a  while. 
Next  remove  from  the  bath  and  connect  with  an  apparatus, 
capable  of  giving  a  rapid  current  of  carbon  dioxide.  The  con- 
nection is  made  by  means  of  a  cork  carrying  two  tubes.  The 
first  dips  below  the  surface  of  the  solution  in  the  flask  and  the 
second  or  outlet  tube  is  bent  downward  and  the  end  dips  slightly 

*  Cf.  Ibbotson  and  Brearley,  Analyst,  1902,  25. 


336  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

below  the  surface  of  some  water  or  mercury.  This  allows  any 
tendency  to  back  pressure  to  be  instantly  detected.  While 
passing  a  rapid  stream  of  gas,  heat  the  contents  of  the  flask  to 
boiling,  using  a  naked  flame,  but  taking  care  to  heat  the  sides  of 
the  flask  and  avoid  directly  heating  the  bottom.  This  is  because 
the  antimony  lies  on  the  bottom  and  the  flask  might  be  cracked 
by  unequal  heating  in  contact  with  solution.  Boil  2-3  minutes 
after  the  liquid  commences  to  boil.  Cool  quickly  by  surrounding 
the  flask  with  cold  water  and  take  care  that  the  current  of  carbon 
dioxide  is  strong  enough  to  prevent  back  pressure  due  to  sudden 
condensation.  When  cold  loosen  the  cork  somewhat  and  intro- 
duce 5  cc.  of  good  starch  solution,  and  then  withdraw  the  flask 
gently  so  as  not  to  allow  air  to  enter  by  forming  currents.  Cork 
quickly  and  take  to  the  burette.  Introduce  the  spit  of  the  burette 
far  down  into  the  neck  of  the  flask  and  rotating  the  latter  gently 
run  in  or  drop  in  N/io  iodine  solution.  Towards  the  end  the 
starch  blue  will  appear  and  remain  mostly  in  the  middle  portion 
of  the  solution,  requiring  stronger  agitation  to  mix  with  the  rest  oi 
the  solution.  This  causes  the  metallic  antimony  in  the  bottom 
of  the  flask  to  become  stirred  up  and  slightly  obscure  any  slight 
blue  tint.  For  this  reason  the  titration  is  continued  till  the  last 
drop  gives  a  strong  blue  to  the  whole  solution,  and  then  we  deduct 
about  0.05  cc.  from  the  burette  reading.  Do  not  fear  that  the 
end  point  will  not  be  recognized  within  one  drop  or  less.  It  is 
unmistakable  with  good  starch  solution,  and  no  doubtful  ending 
should  be  taken.  With  correct  solutions,  etc.,  the  titration 
should  have  taken  just  20.00  cc.  Mixtures  of  C.P.  antimony 
and  C.P.  tin  (allowing  for  o.io  per  cent,  impurities  found  to  be 
present)  give  exact  results.  No  trouble  has  been  found  in  titrating 
tin  correctly  with  iodine.  Objections  to  this  method  may  be 
founded  on  accepting  C.P.  tin  as  actually  nothing  but  tin,  while 
most  of  it  contains  impurity. 


M  ISC  ELLA  NEOUS. 


337 


To  test  tin  or  antimony  for  impurity,  a  quick  method  of  con- 
siderable accuracy  is  to  take  about  o.  5  gram  in  a  porcelain  boat, 
place  in  a  combustion  tube  and  pass  a  slow  current  of  dry  chlorine 
and  dry  hydrochloric  acid  gas.  The  tin  or  antimony  is  quickly 
volatilized  and  lead,  copper,  iron,  etc.,  remain  mostly  in  the  boat. 
Displacing  the  chlorine  with  carbon  dioxide  and  then  heating  in 
a  current  of  hydrogen  reduces  the  chlorides  left  in  the  boat  to 
metal,  and  their  weight  can  be  deducted  from  the  original  metal, 
or  the  percentage  determined.  This  is  not  strictly  accurate,  as 
on  first  heating  in  hydrogen  there  is  a  slight  volatilization  of  some 
of  the  chlorides. 

In  the  case  of  an  alloy  a  good  qualitative  analysis  should  always 
be  made,  unless  the  approximate  composition  is  known.  If  there 
are  no  interfering  metals,  the  alloy  is  decomposed  and  the  anti- 
mony and  tin  titrated,  as  shown  above,  without  removing  the 
lead  sulphate,  copper  sulphate,  etc.  Lead  in  large  amount  does 
not  interfere.  Theoretically,  any  amount  of  copper  should  not 
interfere,  and  practically  small  amounts  are  known  to  cause  no 
trouble,  while  large  amounts  have  not  been  present  in  the  tests 
made.  Should  the  alloy  contain  iron  in  any  quantity,  there  might 
be  some  danger  of  ferrous  sulphate  being  left  after  boiling  with 
sulphuric  acid.  This  difficulty  is  overcome  by  decomposing 
the  alloy  with  nitric  acid,  as  usual,  boiling  off  most  of  the 
nitric  acid,  adding  about  10  cc.  of  sulphuric  acid  and  3-4  grams 
potassium  sulphate,  boiling  to  complete  expulsion  of  the  nitric 
acid,  and  then  adding  a  little  tartaric  acid  or  other  organic  matter, 
and  after  the  carbonization,  continuing  the  boiling  till  all  organic 
matter  has  been  destroyed.  This  will  always  leave  the  antimony 
and  tin  in  the  "  ous  "  and  "  ic  "  states,  respectively.*  From  this 
point,  the  determination  is  carried  on  in  the  manner  described 

*  A.  H.  Low,  Jour.  Am.  Chem.  Soc.,  XXVIII,  1715. 


338  TECHNICAL  METHODS  OF   ORE   ANALYSIS. 

above.  Where  the  antimony  and  tin  have  been  separated  from 
the  other  metals  by  means  of  alkaline  sulphides,  the  details  of 
operation  depend  on  whether  the  decomposition  of  the  alloy  was 
made  with  aqua  regia  or  with  sulphuric  or  nitric  acid.  It  will  be 
assumed  that  the  alloy  has  been  dissolved  in  aqua  regia  and  the 
tin  and  antimony  are  in  solution  combined  with  alkaline  sulphides. 
Add 'slight  excess  of  sulphuric  acid  and  heat  gently  to  precipitate 
the  sulphides  of  antimony  and  tin.  Filter,  preferably  through 
a  60  mm.  Witt's  plate  and  an  S.  &  S.  white  ribbon  filter  No.  589, 
and  wash  the  precipitate  on  the  filter  with  dilute  hydrogen  sulphide 
water  containing  enough  ammonium  acetate  to  prevent  stannic 
sulphide  from  giving  a  turbid  or  opalescent  filtrate.  After  wash- 
ing somewhat,  test  each  succeeding  10-20  cc.  of  filtrate  by  boiling 
off  the  hydrogen  sulphide,  acidifying  with  nitric  acid  and  adding 
three  or  four  drops  of  silver  nitrate  solution.  The  last  filtrate 
should  be  entirely  free  from  chlorine,  as  shown  by  this  test.  With 
a  Witt's  plate  of  60  mm.  diameter,  this  is  quickly  accomplished. 
The  residue  on  the  filter  and  filter  itself  may  now  be  placed  in  a 
450  cc.  Jena  glass  Erlenmeyer  flask,  3-4  grams  potassium  sulphate 
added  and  10-20  cc.  strong  sulphuric  acid,  and  the  whole  mass 
boiled  till  all  organic  matter  has  been  destroyed  and  the  antimony 
and  tin  are  present  as  sulphates,  while  there  are  not  over  10  cc.  of 
free  sulphuric  acid  left  in  the  flask.  As  organic  matter  is  not 
really  necessary  in  this  operation,  and  it  takes  some  time  to  oxidize 
the  filter  paper,  the  precipitate  on  the  filter  can  be  handled  differ- 
ently, if  some  alkaline  sulphide,  free  from  chlorine  compounds, 
is  available.  This  desideratum  will  probably  be  found  best  in 
ammonium  sulphides  or  poly-sulphides,  as  the  best  C.P.  by 
alcohol  caustic  soda  contains  enough  chloride  to  cause  some  loss 
of  tin.  The  precipitate  is  washed  from  the  filter  into  the  flask 
with  as  small  a  quantity  of  water  as  possible.  What  remains  on 
the  filter  is  dissolved  off  with  alkaline  sulphide  free  from  chlorine 


MISCELLANEOUS.  339 

and  the  solution  added  to  the  flask.  Enough  alkaline  sulphide 
is  now  added  to  the  flask  to  dissolve  the  sulphides  of  antimony  and 
tin  on  warming.  When  this  is  accomplished,  acidify  with  sul- 
phuric acid  and  then  add  about  10-15  cc*  m  excess  and  3-4  grams 
potassium  sulphate  and  boil  down  to  sulphuric  acid  fumes  and  till 
all  sulphur  has  been  expelled  and  the  antimony  and  tin  remain 
only  as  sulphates.  The  final  amount  of  free  sulphuric  acid  left 
should  not  be  over  10  cc.  Tin  tends  to  form  a  stannic  sulphate, 
very  insoluble  in  strong  sulphuric  acid,  but  subsequent  heating 
and  boiling  in  the  presence  of  hydrochloric  acid  dissolves  it.  The 
boiling  with  strong  sulphuric  acid  and  destruction  of  organic 
matter  is  carried  on  easily  and  quickly  over  a  naked  flame  of  good 
heating  power.  The  Jena  glass  Erlenmeyer  flasks  stand  the 
operation  very  well,  and  none  have  cracked.  The  flask  is  gen- 
erally held  in  the  hand  by  means  of  a  clamp  (Chaddocks'  clamp 
with  rubber  removed  is  very  good)  and  rotated  to  insure  even 
heating.  In  this  way  the  sulphuric  acid  may  be  completely 
driven  off,  leaving  a  melt  of  acid  potassium  sulphate,  and  the 
flask  will  not  break.  If  there  is  any  doubt  that  the  antimony 
does  not  exist  in  the  "  ous  "  condition,  a  little  tartaric  acid  or 
other  organic  matter  may  be  added  and  burned  off  by 
boiling.  The  antimony  and  tin  now  exist  as  sulphate  and 
the  procedure  is  the  same  as  in  the  standardization  of  the 
permanganate. 

This  method  for  the  sulphides  of  antimony  and  tin  is  in  every 
way  much  more  satisfactory  than  the  gravimetric  separation  and 
determination,  and  takes  little  time. 

Mixtures  of  C.P.  antimony  and  tin  (allowing  for  any  im- 
purities) give  exact  results.  An  alloy  run  through  recently 
gave  the  following  results.  Qualitative  analysis  showed  the 
metals  indicated  to  be  the  only  ones  present,  except  in  minute 
traces, 


340  TECHNICAL  METHODS   OF  ORE   ANALYSIS. 

Lead 74-19     Alloy  dissolved  in  aqua  regia,  alkaline  sulphide 

separation,  lead  separated  from  copper  as 
sulphate  in  presence  of  alcohol.  Two 
determinations  checked. 

Antimony 15-44       Alloy  boiled  with  sulphuric  acid  and  antimony 

titrated  direct,  as  in  standardizing  perman- 
ganate. 

Tin     9.88      Determined  in  same  solution,  after  the  anti- 
mony. 

Copper 0.44  Determined  after  the  lead,  driving  off  alcohol 

and  determining  by  A.  H.  Low's  iodide 
process.  Check  test. 

Iron    .  trace 


99-95 

If  arsenic  were  present,  it  would  interfere  with  the  antimony 
titration  or  be  counted  as  antimony.  It  may  easily  be  removed. 

It  is  often  stated  that  the  titration  of  tin  with  iodine  gives 
slightly  low  results.  Experience  with  the  above  method  has 
given  confidence  that  the  results  for  tin  are  exact,  if  the  conditions 
are  observed.  Tin  may  be  lost  somewhere  in  the  process,  but 
all  that  remains  is  surely  indicated  by  the  titration. 

Method  of  A.  Rossing  for  Separation  of  Sulphides.  *  —  In  this 
method  the  alloy  is  dissolved  in  a  minimum  of  aqua  regia,  using 
a  little  potassium  chlorate  to  insure  complete  oxidation.  After 
some  dilution  a  little  tartaric  acid  is  added,  the  solution  almost 
exactly  neutralized  with  sodium  hydroxide  solution  and  a  suffi- 
cient quantity  of  colorless  sodium  hydrosulphide,  NaSH,  added 
to  precipitate  copper,  lead,  etc.,  and  to  retain  all  the  antimony 
and  tin  in  solution.  By  using  a  gentle  heat  and  with  enough 
sodium  sulphide  the  antimony  and  tin  will  go  into  solution. 
Filter,  washing  the  residue  with  hot  dilute  sodium  sulphide  solu- 
tion. Test  the  final  washings  by  acidifying  them,  to  make  sure 
of  the  removal  of  all  the  antimony  and  tin  from  the  residue. 

*  Jour.   Soc.  Chem.  Ind.,  1902,  191. 


TABLES. 


RELATION   OF    BAUME   DEGREES   TO    SPECIFIC   GRAVITY,   FOR 
LIQUIDS  LIGHTER  THAN  WATER. 


Baume". 

Specific 
Gravity. 

Baume1. 

Specific 
Gravity. 

Baume. 

Specific 
Gravity. 

Baurne". 

Specific 
Gravity. 

10 

I  .  OOOO 

31 

0.8695 

52 

0.7692 

73 

0  .  6896 

ii 

0.9929 

32 

0.8641 

53 

0.7650 

74 

0.6863 

12 

0.9859 

33 

o  .  8588 

54 

0.7608 

75 

o  .  6829 

*3 

0.9790 

34 

0.8536 

55 

0.7567 

76 

o  .  6796 

14 

0.9722 

35 

o  .  8484 

56 

0.7526 

77 

0.6763 

15 

o-9655 

36 

0.8433 

57 

o  .  7486 

78 

o  .  6730 

16 

0.9589 

37 

0.8383 

58 

o  .  7446 

79 

0.6698 

17 

o-9523 

38 

°-8333 

59 

o  .  7407 

80 

0.6666 

18 

0.9459 

39 

0.8284 

60 

0.7368 

81 

0.6635 

iQ 

o-9395 

40 

0.8235 

61 

0.7320 

82 

0.6604 

20 

o-9333 

4i 

0.8187 

62 

0.7290 

83 

0-6573 

21 

0.9271 

42 

0.8139 

63 

0.7253 

84 

o  .  6542 

22 

0.9210 

43 

0.8092 

64 

0.7216 

85 

0.6511 

23 

0.9150 

44 

o  .  8045 

65 

0.7179 

86 

0.6481 

24 

o  .  9090 

45 

o  .  8000 

66 

0.7142 

87 

0.6451 

25 

0.9032 

46 

0-7954 

67 

0.7106 

88 

o  .  6422 

26 

0.8974 

47 

o  .  7909 

68 

o  .  7070 

89 

o  .  6392 

27 

0.8917 

48 

0.7865 

69 

o  -  7035 

90 

o  .  6363 

28 

o  .  8860 

49 

0.7821 

70 

o  .  7000 

95 

0.6222 

29 

0.8805 

5° 

0.7777 

7i 

o  .  6965 

3° 

0.8750 

5i 

0-7734 

72 

0.6930 

341 


342  TABLES. 

TABLE  OF  MEASURES  AND  WEIGHTS. 

MEASURES  OF  CAPACITY. 

A.  Dry  Measure. 

i  bushel  =2150.42  cubic  inches. 

i     "        =  the  volume  of  77. 62  7  pounds  of  distilled  water  at  4°C. 
Legal:  i  liter  =  0.908  quart. 

I  bushel  =  4  pecks  =  8  gallons  =  32  quarts  =  3 5. 2 42 2 9  liters. 

I  peck  =2  gallons  =   8  quarts  =   8.81057  liters. 

i  gallon  =   4  quarts  =   4.40528  liters. 

i  quart  =    1.10132  liters. 

B.  Liquid  Measure. 
i  U.  S.  gallon  =231  cubic  inches, 
i  gallon  =  the  volume  of  8.3388822  pounds  =  58378  troy  grains  of  distilled  water  at 

4°  C.     (Stillman,  Engineering  Chemistry.) 
i    "       =58318  grains  of  water  at  62°  F.     (U.  S.  Phar.) 

1  "  =58334-9+  grains  of  pure  water  at  60°  F.,  weighed  in  air  at  60°  F.,  at 
barometric  pressure  of  30  inches  of  mercury.  (Mason,  Examination 
of  Water.) 

Legal:  i  liter  =1.05 67  quart  =  0.2 64 17  gallon, 
i  gallon  =  4  quarts  =  8  pints  =32  gills  =  3. 785 44  liters, 
i  quart  =2  pints  =  8  gills  =  0.94 63 6  liter, 
i  pint    =  4  gills  =  0.47318  liter. 

i  gill  =0.118295  liter. 

I  cubic  foot  =  7.48  gallons  =  28.3 1 5  liters  =  62 .42  pounds  of  water  at  60°  F.     (Still- 
man.) 

i  cubic  foot  of  water  at  62°  F.  =  62.355  pounds  avoirdupois  =  28320  grams, 
i  cubic  inch   of   water  at   62°   F.  =0.0361    pounds   avoirdupois  =  16.387   grams. 
(Watts'  Dictionary,  V,  1010.) 

Linear  Measure. 

i  yard  =0.91440  meter, 
i  foot  =0.30480  meter, 
i  inch  =  0.0254  meter. 
39.37  inches  =  i  meter. 

WEIGHTS. 

I  grain  troy   =0.0648004  gram. 

l  pound  troy  =  0.822857  pounds  avoirdupois. 

i  pound  avoirdupois  =  7000  grains  troy  =  1.215279  pounds  troy. 


TABLES.  .343 

Troy  Weight. 

I  pound=i2  oz.  =  24o  pwts.  =  57<5o  grains  =  373. 2418  grams. 

I  oz.=   20  pwts.  =  480  grains  =  31.1035  grams. 

i  pwt.  =     24  grains  =      1.5552  grams. 

i  grain  =     0.0648  grams. 

i  gram  =  15.432  troy  grains. 

Avoirdupois  Weight. 

I  ton  =  20  hundred  weight  =  2  240  pounds  =  1016.04  kilograms, 
i  hundredweight  =    112  pounds  =     50.80  kilograms. 
I  pound  =  16  ounces  =256  drams  =  7000.00  grains  =  453.5900  grams, 
i  ounce    =16  drams  =  437.50  grains  =  28.3495  grams, 
i  dram     =     27. 34  grains  =     1.7718  grams, 
I  net  ton«=2ooo  pounds  =  29166!  ozs.  troy  =  907. 19  kilograms. 

Metric  Ton. 
I  metric  ton  =  1000  kilograms. 

CONVERSION  OF  THERMOMETER  READINGS. 

To  convert  Fahrenheit  to  Centigrade,  subtract  32  and  multiply  by  f . 
To  convert  Centigrade  to  Fahrenheit,  multiply  by  f  and  add  32. 


344  TABLES. 

INTERNATIONAL  ATOMIC  WEIGHTS,  1908.* 


Aluminum    Al 

Antimony   Sb 

Argon    A 

Arsenic    As 

Barium   Ba 

Bismuth    Bi 

Boron B 

Bromine Br 

Cadmium Cd 

Caesium Cs 

Calcium Ca 

Carbon C 

Cerium Ce 

Chlorine Cl 

Chromium Cr 

Cobalt .Co 

Columbium Cb 

Copper Cu 

Erbium Er 

Europium Eu 

Fluorine F 

Gadolinium Gd 

Gallium Ga 

Germanium    Ge 

Glucinum Gl 

Gold Au 

Helium He 

Hydrogen H 

Indium    In 

Iodine I 

Indium Ir 

Iron Fe 

Krypton    Kr 

Lanthanum La 

Lead '. Pb 

Lithium Li 

Magnesium Mg 

Manganese Mn 

Mercury Hg 

Molybdenum Mo 


27.  i  Neodymium Nd 

120.2  Neon Ne 

39.9  Nickel Ni 

75 .  o  Nitrogen N 

137 . 4  Osmium Os 

208.0  Oxygen O 

n.o  Palladium Pd 

79 . 96  Phosphorus P 

112.4  Platinum Pt 

132 . 9  Potassium     K 

40 .  i  Praseodymium     Pr 

12. o  Radium Rd 

140. 25  Rhodium Rh 

35 . 45  Rubidium Rb 

52 .  i  Ruthenium Ru 

59 .  o  Samarium Sa 

94 .  o  Scandium Sc 

63 . 6  Selenium Se 

166.0  Silicon Si 

152.0  Silver     Ag 

19 .  o  Sodium     Na 

156.0  Strontium Sr 

70 .  o  Sulphur     S 

72.5  Tantalum Ta 

9.1  Tellurium Te 

197.2  Terbium Tb 

4.0  Thallium Tl 

i .  008  Thorium Th 

115.0  Thulium... Tm 

126.97  Tin Sn 

193 .  o  Titanium Ti 

55.9  Tungsten W 

81 . 8  Uranium U 

138.9  Vanadium V 

206.9  Xenon Xe 

7 . 03  Ytterbium Yb 

24.36  Yttrium Yt 

55 .  o  Zinc Zn 

200.  o  Zirconium Zr 

96.0 


143-6 

2O.O 

58-7 

i4-oi 
191.0 

i6.o 
106.5 

31.0 
194.8 

39.15 
140.5 

225.0 
103.  o 

85.5 
101.7 

44.1 

79.2 

28.4 

107.93 

23  -°5 
87.6 
32.06 
181.0 
127.6 
159.2 
204.1 

232-5 
171.0 
119. 

48. 
184. 
238, 


128 
173.0 
89.0 

65.4 
90.6 


*  These  are  the  atomic  weights  used  throughout  this  book.  For  technical 
work  it  was  not  deemed  necessary,  at  present,  to  adopt  the  latest  figures,  since 
the  changes  they  would  produce  in  results  are  very  slight. 


TABLES. 
INTERNATIONAL  ATOMIC    WEIGHTS,  1910. 


345 


Symbol 

Atomic 
Weight. 

Symbol 

Atomic 
Weight 

Aluminium 

Al 

27.1 

Molybdenum.  . 

Mo 

96   0 

Antimony 

Sb 

120  2 

Neodymum 

Nd 

144  3 

Argon 

A 

39  9 

Neon 

Ne 

20  0 

Arsenic  

As 

74.96 

Nickel  

Ni 

58  68 

Barium     

Ba 

137.37 

Nitrogen  

N 

14  01 

Bismuth        

Bi 

208.0 

Osmium  

Os 

190  9 

Boron 

B 

11  0 

Oxygen 

o 

16  00 

Bromine 

Br 

79  92 

Palladium 

Pd 

106  7 

Cadmium  

Cd 

112.40 

Phosphorus  

P 

31  0 

Caesium       

Cs 

132.81 

Platinum  

Pt 

195  0 

Calcium 

Ca 

40  09 

Potassium 

K 

39  10 

Carbon 

c 

12  00 

Praseodymium   . 

Pr 

140  6 

Cerium     

Ce 

140.25 

Radium  

Ra 

226  4 

Chlorine         

Cl 

35  46 

Rhodium  

Rh 

102  9 

Chromium 

Cr 

52  0 

Rubidium  

Rb 

85  45 

Cobalt  

Co 

58.97 

Ruthenium  

Ru 

101  7 

Columbium  

Cb 

93.5 

Samarium  

Sa 

150  4 

Copper 

Cu 

63  57 

Scandium  

Sc 

44  1 

Dysprosium  

Dy 

162.5 

Selenium  

Se 

79  2 

Erbium        

Er 

167.4 

Silicon  

Si 

28  3 

Europium 

Eu 

152.0 

Silver  

As 

107  88 

Fluorine 

F 

19  0 

Sodium       

Na 

23  00 

Gadolinium  

Gd 

157.3 

Strontium  

Sr 

87  62 

Gallium 

Ga 

69.9 

Sulphur  

s 

32  07 

Germanium 

Ge 

72.5 

Tantalum  

Ta 

181  0 

Glucinum  * 

Gl 

9  1 

Tellurium  

Te 

127  5 

Gold 

Au 

197  2 

Terbium       

Tb 

159  2 

Helium        

He 

4/0 

Thallium  

Tl 

204  0 

Hy  d  rogen 

H 

1  008 

Thorium 

Th 

232  42 

Indium 

In 

114  8 

Thulium  

Tm 

168  5 

Iodine 

I 

126  92 

Tin       

Sn 

119  0 

Indium        

Ir 

193.1 

Titanium  

Ti 

48  1 

Iron 

Fe 

55.85 

Tungsten  

W 

184  0 

Krypton 

Kr 

83  0 

Uranium  

U 

238  5 

Lanthanum 

La 

139  0 

Vanadium 

V 

51  2 

Lead          

Pb 

207.10 

Xenon  

Xe 

130  7 

Lithium 

Li 

7  00 

Ytterbium 

Lutecium  

Lu 

174.0 

(Neoytterbium)  . 

Yb 

172.0 

Magnesium 

Me 

24  32 

Yttrium 

Yt 

89  0 

Manganese 

Mn 

54  93 

Zinc 

Zn 

65  37 

Mercury       

Hg 

200.0 

Zirconium  

Zr  ' 

90  6 

Also  called  Beryllium,  Be. 


346  TABLES. 

CHEMICAL  FACTORS  AND  THEIR  LOGARITHMS. 


Weighed. 

Required. 

Factor. 

Log.* 

Aluminum             •  . 

ALO, 

Al 

O     ^  7O  7. 

97245 

A1PO4  

ALO, 

o  4185 

9621  7 

Antimony          

Sb 

o  7807 

o  8075 

As  So 

As 

97848 

AsoO, 

MCT  ASoOy  

As 

o  4827 

ASnO, 

O    6772 

tt 

ASoOr 

o  7402 

o  860.1 

BaSO4  

Ba 

o  5885 

o  7608 

BaO 

o  6570 

9  8176 

BaCO3.  .  

Ba 

o  6960 

9  8426 

BaO 

O    7771 

9800  ? 

BaCrO4  

Ba 

o   ^4.20 

9774O 

BaO 

o  7818 

Bismuth              .  .  . 

BioO,  . 

Bi 

o  8966 

9CK26 

BiOCl  

Bi 

o  8017 

9QO4O 

BioO, 

o  8041 

9  95*3 

Bromine       •    

AgBr  

Br 

o  4256 

96200 

HBr 

0.4700 

96744 

Cadmium.  

CdO  

Cd 

90422 

CdS  

Cd 

0.7780 

Q8oio 

CdO 

o  8888 

o  oj.88 

CdSO4    

Cd 

97717 

Calcium 

CaO         

Ca 

O    714.8 

98^4.2 

CaCO3  

Ca 

c  4006 

96O27 

CaO 

o  ^604 

974.8  5 

CaSO4   

Ca 

O    2Q4? 

• 

CaO 

o  4120 

96140 

Carbon  

CO,  

c 

0.2727 

Chlorine    

AffCl  .  . 

Cl 

O    2472 

O     7O7 

HC1 

O    2  CC4.3 

0    40  C  7 

Ac  .  . 

Cl 

9   5165 

HC1 

Cr  O 

Cr 

o  6846 

<2<    * 

CrO» 

It 

CrO 

PbCrO4 

Cr 

o  161  7 

9  2076 

CrO, 

O    7OOO 

9401  3 

tt 

CrO4 

o   3^94 

9  5556 

BaCrO4  

Cr 

o  .  2055 

9.3129 

CrO, 

O  .  3Q4Q 

9.5964. 

ii 

CrO4 

o  4^80 

0.66oo 

Cobalt             .  .    . 

Co 

CoO 

i   2712 

o.  1042 

CoSO4  

Co 

0.780; 

9.5804 

CoO 

0.4838 

9.6846 

Cu  

CuO 

i  .  2516 

0.0974 

CuO     

Cu 

o  .  7900 

9.9025 

Cu2S     

Cu 

0.7987 

9.9024 

CuO 

0.9996 

9.9999 

Cu,(CNS),.  . 

Cu 

o.  "5229 

9.7184 

*  The—  TO  after  the  logarithms  is  omitted. 


TABLES.  347 

CHEMICAL  FACTORS  AND   THEIR  LOGARITHMS— Continued. 


Weighed. 

Required. 

Factor. 

Log. 

CaF2 

F 

o  4866 

o  6871 

Hydrogen  
Iodine        

H2O  
Ael 

H 
I 

0.1119 
o   ^40? 

9.0488 
o  7328 

<  < 

HI 

o.  ^448 

9.7362 

FeoO,. 

Fe 

o  .  6006 

Q  .  8440 

FeO 

o  8000 

9QCA2 

Lead        

pbO             

Pb 

o  0282 

9Q676 

pbO2          

Pb 

o  8660 

9O37^ 

pbS            

Pb 

o  8658 

90374 

<  < 

PbO 

0.0328 

o  0608 

PbSO 

Pb 

o  6820 

PbO 

O.7-JC7 

9  8667 

pbC!2               

Pb 

0.7447 

9872O 

i  t 

PbO 

0.8024 

9QO44 

PbCrO4      

Pb 

0.6406 

9  8066 

PbO 

0.6901 

o  8380 

M^agnesium  .    

MgO   

Mg 

0.6036 

Q  7807 

Mg,P9O7.  . 

Mg 

0.2187 

0.  3390 

MgO 

0.3624 

0-  ^02 

MffSO. 

Mg 

O    2O2  3 

93060 

MffO 

O    33^2 

9C2  52 

^Manganese        ...... 

Mn3O4   

Mn 

O    72O^ 

Q    8?76 

« 

MnO 

O  .  Q3O  I 

o  068  q 

MnS  

Mn 

O.6?I7 

0  .  800  Z 

«  « 

MnO 

b.8z<< 

Q.QII4 

Mn0P0O7.  . 

Mn 

0.3873 

0.  ">88o 

MnO 

o  5000 

o  6000 

MnSO4    

Mn 

o   3641 

o  <6i2 

«  < 

MnO 

o  .4700 

0.6721 

Hg  . 

HgO 

I  .  0800 

0.0334 

HgS  

Hg 

0.8618 

9.Q354 

i  4 

HgO 

o  0308 

HgCl    . 

Hg 

o  8404 

0.02QI 

HeO 

O  01  74 

0.0626 

MoO3  

Mo 

o  6667 

9.8239 

Nickel 

Ni 

NiO 

I    2726 

O    I  O47 

NiO 

Ni 

o  78<;8 

o  80^3 

NiSO4  . 

Ni 

O    3703 

0    ^70O 

t  i 

NiO 

o  4827 

o  6837 

(NH/),PtCL  . 

N 

o  0630 

8.7QQ3 

NH3 

o  0767 

8.8848 

<  < 

NH4 

o  0812 

8.9096 

Pt     

N 

0.1438 

0-1577 

<  « 

NH3 

O.I749 

9.  2427 

<  « 

NH4 

0.1852 

9.2677 

Phosphorus  

Mg,P2O7.  . 

P 

0.2784 

a 

9  .  4440 

i  i 

PO4 

O.8^3I 

9.9310 

t  < 

PoO* 

6   6376 

o  804^ 

(NH4)3P04.i2Mo03. 
(i 

P 
P04 
P;05 

0.0165 
0.0506 
0.0378 

8.2178 

8.7042 
8-5777 

348  TABLES. 

CHEMICAL   FACTORS   AND  THEIR   LOGARITHMS— Continued. 


Weighed. 

Required. 

Factor. 

Log. 

KC1  

K 

O    C24.S 

972OO 

«  ( 

K2O 

o  6320 

9   800  7 

K  PtCl 

K 

K  O 

•  ^°/v5 
o  2880 

K  SOA            .  . 

K 

K  O 

•  uo^o 

Selenium  

Se  

SeOo 

I    4040 

•  /oo1 
O    1474 

Silicon  .  

SiO 

Si 

9672  3 

Silver     

AeCl 

^ff 

o   7^28 

9  8766 

AgBr 

A! 

97CQ2 

A  2! 

\2 

O    4.^07 

9662  < 

AffoS 

A! 

O    87O7 

9O^OQ 

NaCl      

Na 

O     3.Q4O 

9CQC  C 

it 

NanO 

o   ^  308 

9724Q 

Na2SO4  

Na' 

O    2.°4.'? 

9^IOQ 

Na9O 

o  4368 

9640^ 

Na  CO, 

Na 

9  6380 

Na  O 

o  ?8<?  ^ 

97674. 

Strontium  

SrC03  

«  < 

Sr 
SrO 

o-5935 
o  ^641 

9-7734 

98d.6'^ 

SrSO4         

Sr 

O   4.77O 

o  678^ 

ii 

SrO 

o   ^13 

97r  i  •? 

Sulphur  

BaSO4  

s 

O    I  T.TI 

O    I  ^77 

«  < 

SO2 

o  274.4. 

94.^84. 

« 

SO3 

O    ^42Q 

Q    e?3l?2 

<  < 

so 

O    4.1  1  ^ 

9614.7 

i  i 

H2SO4 

o  4201 

962  T.T. 

Tin  

SnO2    

Sn 

0.7880 

o  8o6t: 

Titanium   .......... 

TiO2            

Ti 

0.6005 

Q    7'78< 

Uranium.  *  

CUOo^PoO,  .  . 

u 

0.6671 

y  •  /  /•-'^ 
9.8242 

«  < 

UoOo 

o   7877 

o  8064 

U,Oe 

u 

o  8482 

o  028? 

Zinc  

ZnO   

Zn 

o  803^ 

900^0 

ZnS    

Zn 

o  6710 

Q    8267 

<  « 

ZnO 

O    8^i?2 

0.0218 

TABLES. 
LOGARITHMS. 


349 


Natural 
Numbers. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

PROP 

9 

3RTIONAL  PARTS. 

123 

4567 

8 

9 

10 

0000 

0043 

0086 

0128 

0170 

0212 

0253 

0294 

0334 

0374  4  8  l 

2  17  21  25  2< 

)3f 

!  37 

11 

0414 

0453 

0492 

0531  0569 

0607 

0645 

0682 

0719 

0755  4  8  1 

I  15  19  23  26  3( 

)34 

12 

0792 

0828 

0864 

0899^0934 

0969 

1004 

1038 

1072 

1106  3    7   1 

3  14  17  21  24 

t2£ 

31 

13 

1139 

1173 

1206 

1239:1271 

1303 

1335 

1367 

1399 

1430  3  6  1 

3  13  16  19'2C 

2f 

29 

14 

1461 

1492 

1523 

1553 

1584 

1614 

1644 

1673 

1703 

1732  3  6    « 

3  12  15  1821 

24 

127 

15 

1761 

1790 

1818 

1S47 

1875 

1903 

1931 

1959 

1987 

2014  3  6    j 

J  11  14  17  2C 

22 

25 

16 
17 

2041 
2304 

2068 
2330 

2095  2122  214L 
2355  23SO  2405 

2175 
2430 

2201 
245.5 

2227 
24SO 

2253 
2504 

2279  3   5    J 
2529  2   5    : 

J  11  13  16  IS 
'  10  12  15  17 

21 
2C 

2 

IS 

2553 

2577 

2601 

2625  264^- 

2672 

2695 

2718 

2742 

2765  2   5    ; 

'    91214161921 

19 

2738 

2310 

2833 

2856 

287C 

2900 

2923 

2945 

2967 

2989  2   4    : 

'    9  11  13'l6 

18 

20 

20 

3010 

3032 

3054 

3075 

3096 

3118 

3139 

3160 

3181 

3201  2  4    ( 

>    8  11  13  15 

17 

19 

21 

32223243 

3263 

3284'3304 

3324 

3345 

3365 

33853404  2  4    ( 

5    S  10  12  14 

16  18 

22 

34243444 

3464 

3483^3502 

3522 

3541 

3560 

3579  3598  2   4    ( 

5    S  10  12  14  15  17 

23 

3617 

3636 

3655 

3674  '3692 

3711 

3729 

3747 

37663784  2  4    ( 

5    7    9  1113  15!17 

24 

3802 

3820 

3838 

3856 

3874 

3892 

3909 

3927 

3945 

3962  2   4    ^ 

>    7    9  11  12 

14  16 

25 

3979 

3997 

4014 

4031 

4048 

4065 

4082 

4099 

4116 

4133  2   3    ^ 

>    7    9  10  12 

14'l5 

26 

4150 

4166 

4183 

4200  4216 

4232 

4249 

4265 

4281 

4298  2   3    i 

>    7    8  10  11  13  15 

27 

4314 

4330 

4346 

4362  4378 

4393 

4409 

4425 

4440,4456  2   3    i 

>    6    8    911  1314 

23 

4472 

44S7 

4502 

4518  4533 

4548 

4564 

4579 

4594  4609  2   3    £ 

»    6    8    911  1214 

29 

4624 

4639 

4654 

4669 

4683 

4698 

4713 

4728 

4742 

4757  i   3    4 

6    7    9  10 

12 

13 

30 

4771 

4786 

4800 

4814 

4829 

4843 

4857 

4871 

4886 

4900  i   3    4 

6    7    9  10 

11 

13 

31 

4914 

4928 

4942 

4955  4969 

4983 

4997 

5011 

5024 

5038  i   3    4 

6    7    8  10  11  12 

32 

5051 

5065 

5079 

5092  5105 

5119 

5132 

5145 

5159 

5172  i   3    4 

5   7    8    911  12 

33 

5185 

5198 

5211 

5224'  5237 

5250 

5263 

5276 

5289 

5302  i   3    4 

5    6    8    9  10  12 

34 

5315 

5328 

5340 

5353 

5366 

5378 

5391 

5403 

5416 

5428  i   3    4 

5689 

10 

11 

35 

5441 

5453 

5465 

5478 

5490 

5502 

5514 

5527 

5539 

5551  i  2    4 

5679 

10 

11 

36 

5563 

5575 

55S7 

5599 

5611 

5623 

5635 

5647 

5658 

5670  i   2    4 

5    6         81011 

37 

56^2 

5694 

5705 

5717 

5729 

5740 

5752 

5763 

5775 

6786  i  2    3 

56         8 

910 

38 

5798 

5809 

5821 

5832 

5843 

5855 

5866 

5877 

5888 

5899  i   2    3 

56         8 

9  10 

39 

5911 

5922 

5933 

5944 

5955 

5966 

5977 

5988 

5999 

6010  1    2     3 

45         8 

9 

10 

40 

6021 

6031 

6042 

6053 

6064 

6075 

6085 

6096 

6107 

6117  123 

4         68 

9 

10 

41 

6128 

6138 

6149 

6160 

6170 

6180 

6191 

6201 

6212 

6222  123 

4         67 

8 

9 

42 

6232 

6243 

6253 

6263 

6274 

6284 

6294 

6304 

6314 

6325  1   2    3 

4         67 

8 

9 

43 

6335 

6345 

6355 

6365 

6375 

6385 

6395  6405 

6415 

6425  1   2    3 

4         67 

8 

0 

44 

6435 

6444 

6454 

6464 

6474 

6484 

6493 

6503 

6513 

6522  i   2    3 

4         67 

8 

9 

45 

6532 

6542 

6551 

6561 

6571 

6530 

6590 

6599 

6609 

6618  i   2    3 

4         67 

8 

9 

46 

6628 

6637 

6646 

6656 

6665 

6675 

6684 

6693 

6702 

6712  i   2    3 

4         67 

7 

S 

47 

6721 

6730 

6739 

6749 

6758 

6767 

6776 

6785 

6794 

6803  l   2    3 

4         56 

7 

S 

48 

6812 

6821 

6830 

6839 

6848 

6857 

6866 

6875 

6884 

6893       2    3 

4456 

7 

8 

49 

6902 

6911 

6920 

6928 

6937 

6946 

6955 

6964 

6972 

6981       2    3 

4456 

7 

S 

50 

6990 

6998 

7007 

7016 

7024 

7033 

7042 

7050 

7059 

7067       2    3 

3456 

7 

8 

51 

7076 

7084 

7093 

7101 

7110 

71  r 

7126 

7135 

7143 

7152       2    3 

3456 

7 

8 

52 

^160 

7168 

7177 

718517193 

7202 

7210  7218 

7226 

7235       2    2 

3456 

7 

7 

53 

7243 

7251 

7259  7267 

7275 

7284 

7292 

7300 

7308 

7316  l   2    2 

3456 

6 

7 

54 

7324 

7332 

7340 

734  S 

7356 

7364 

7372 

7380 

7388 

7396  1   2    2 

3456 

6 

7 

350 


TABLES. 


LOGARITHMS. 


1  Natural  I 
Numbers. 

0 

1 

2 

3 

4 

5 

G 

7 

8 

9 

PROPORTIONAL  PARTS. 

1 

? 

3 

4 

5  6 

7 

8  6 

55 

7404 

7412 

7419 

7427 

743£ 

7443 

7451 

7459 

74667474 

1 

2 

2 

3 

4  5 

K 

6  7 

56 

7482 

7490  7497 

7505 

7513 

752C 

7528 

753G  7543  755 

1 

2 

2 

j 

4  5 

5 

6  7 

57 

7559 

75667574 

7582 

7589 

7597 

7604 

7612J7C19  762"- 

1 

2 

2 

4  5 

e 

6  7 

58 

7634 

7642  7649 

7657 

7664 

7672 

7679  768G  7694  770 

1 

1 

A 

4  4 

5 

6  7 

59 

7709 

7716 

7723 

7731 

7738 

7745 

7752 

7760 

7767 

7774 

1 

1 

c 

4  4 

5 

6  7 

60 

7782 

7789 

7796 

7803 

7810 

7818 

7825 

7832 

7839  7846 

1 

1 

2 

1  4 

5 

5  6 

61 

7853 

7860 

7868 

7875 

7882 

7889 

789G 

7903 

7910  7917 

1 

1 

2 

3 

1  4 

5 

i  6 

62 

7924 

7931 

7938 

7945 

7952 

7959  7966 

7973 

7980  7987 

1 

1 

2 

3 

3  4 

5  ( 

3  6 

63 
64 

7993 
8062 

8000 
8069 

8007,8014 
8075  8082 

8021 
8089 

8028  8035  8041 
8096'8102  8109 

8048 
8116 

8055 

8122 

1 
1 

1 
1 

2 
2 

3 
3 

3  4 
J  4 

5  « 
5  . 

5  6 

>  6 

65 

8129 

8136 

8142  8149 

8156 

8162  8169  8176 

8182 

8189 

1 

1 

2 

3 

}  4 

5  I 

>  6 

66 

8195820282098215 

8222 

8228  8235  8241  8248  8254 

1 

1 

2 

3 

545* 

>  6 

67 
68 

8261  8267 
83258331 

8274,8280 
8338  8344 

8287 
8351 

8293  8299  8306 
8357  8363  8370 

83128319 
8376  8382 

1 
1 

1 
1 

2 
2 

3 
3 

!  4  5  i 
544^ 

>  6 
>  6 

69 

8388 

8395 

8401 

8407 

8414 

8420  8426 

8432 

8439  8445 

1 

1 

2 

2 

!  4 

4  I 

>  6 

70 

8451 

8457  8463  8470  8476 

8482  8488 

8494 

8500 

8506 

1 

2 

2 

4 

4  £ 

6 

71 

72 

8513  8519  8525  8531 
8573  8579  8585  8591 

8537 

8597 

8543  8549  8555  8561 
8603  8609  8615  8621 

8567 
8627 

1 
1 

2 
2 

2 
2 

4 
4 

4  £ 

4  £ 

5 
5 

73 

8633  8639  8645  S651 

8657 

8663  8669  8675  8681 

8686 

1 

2 

2 

4 

4  L 

5 

74 

8692 

8698 

8704 

8710 

8716 

87228727 

8733 

8739 

8745 

1 

2 

2 

4  4  5 

5 

75 

8751 

8756  8762  8768 

8774 

77987858791 

8797 

8802 

1 

1 

2 

2 

3 

4  5 

5 

76 

77 

8808 
8865 

8814 
8871 

882088258831 
8876  8882  8887 

837  8842  8848 
893  8899  8904 

8854  8859 
89108915 

1 

[ 

j 

2 
2 

2 

2 

3 

4  5 
4  4 

5 
5 

78 

8921 

8927 

8932  8938  8943 

949  8954  8960 

8965  8971 

[ 

1 

2 

2 

3 

4  4 

5 

79 

8976 

8982 

8987  8993  899£ 

004  9009  901  5 

90209025 

1 

-> 

O 

3 

4  4 

5 

80 

031 

9036 

9042 

9047 

9053 

058 

9063 

9069 

9074 

9079 

2 

O 

31 

4  4 

5 

81 

085 

9090 

9096  9101  9106,9112  9117  9122 

912S'9133 

2 

o 

3 

4  4 

5 

82 
83 

138 
191 

9143 
9196 

9149  9154,9159  9165,9170  9175 
9201  9206,9212  9217  9222  9227 

91809186 
92329238 

1 

1 

2 
2 

£ 

3 
3 

4  4 
4  4 

5 
5 

84 

243 

9248 

9253 

9258 

9263 

9269 

9274 

9279 

9284,9289 

1 

1 

2 

2 

3 

4  4 

5 

85 

294 

9299 

9304 

9309 

9315 

9320 

9325 

9330 

93359340 

2 

2 

3 

4  4 

5 

86 

345 

935093559360 

9365 

9370 

9375  9380  9385  9390 

1 

1 

2 

2 

3 

4  4 

5 

87 
88 
89 

395 
445 
494 

9400940594109415 
9450  9455  9460  9465 
9499  9504  9509  9513 

9420 
9469 
951S 

9425 
9474 
9523 

9430 
9479 
9528 

9435  9440 
9484  9489 
9533  9538 

0 
) 
0 

1 

2 

3 
3 
3 

3  4 
3  4 
3  4 

4 
4 
4 

i 

90 

542 

9547  9552  9557  9562 

9566 

9571 

9576 

95  U  9586 

0 

2 

3 

3  4 

4 

91 

9590 

9595960096059609 

9614 

9619  9624 

96289633 

) 

> 

3 

3  4 

92 
93 

963^ 
9685 

96439647,96529657 
9689:969496999703 

9661 
970^ 

9666  9671 
9713  9717 

9675 
9722 

9680 
9727 

0 

) 

• 

1 

) 

3 
3 

3  4 
3  4 

94 

9731 

9736  9741 

9745  9750 

9754 

9759  9763 

9768 

9773 

0 

1 

1 

2 

3 

3  4 

95 

9777 

9782 

9786 

97919795 

9800 

9805  9809 

9814 

9818 

0 

1 

1 

> 

3 

3  4 

96 

9823 

9827  9832  9836  9841 

9S45  9850  9854  9859 

9863 

0 

1 

1 

> 

3 

3  4 

97 

9868 

987298779881  9886 

9890989498999903 

9908 

0 

1 

1 

> 

3 

3  4 

98 

9912 

9917992199269930 

9934  9939  9943  9948 

9952 

o 

1 

1 

0 

3 

3  4 

99 

9956 

9961  9965  9969  9974 

9978  9983 

9987 

9991 

9996 

0 

1 

1 

> 

3 

3  2 

t  4 

TABLES. 
ANTILO  G  ARITH  MS. 


351 


Logarithms. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

PROPORTIONAL  PARTS. 

1 

2 

3 

4 

5 

6 

7 

8 

'9 

.00 

1000 

1002 

1005  1007 

1009 

1012  1014 

1016 

1019 

1021 

0 

0 

1 

1 

1 

1 

2 

2 

2 

.01 

1023 

1026  1028J  1030 

1033 

1035  1038 

1040 

1042 

1045 

0 

0 

1 

1 

1 

1 

2 

2 

A 

.02 

1047 

1050  1052  1054 

1057 

1059  1062 

1064 

1067 

1069 

0 

0 

1 

1 

1 

1 

2 

2 

2 

.03 
.04 

1072 
1096 

1074  10761079!  1081 
1099110211041107 

1084  1086 
11091112 

1089 
1114 

1091 
1117 

1094 
1119 

0 
0 

0 

1 

1 
1 

1 
1 

1 
1 

1 
2 

2 
2 

2 

2 

2 
2 

.05 

1122 

112511271130 

1132 

11351138 

1140 

1143 

1146 

0 

1 

1 

1 

1 

2 

2 

2 

2 

.06 

1148 

1151  11531156 

1159 

1161  1164 

1167 

1169 

1172 

0 

1 

1 

1 

1 

2 

2 

2 

2 

.07 

1175 

1178  1180  1183 

1186 

11891191 

1194 

1197 

1199 

0 

i 

I 

1 

1 

2 

2 

2 

2 

.08 

1202 

120512081211 

1213 

12161219 

1222 

1225 

1227 

0 

1 

1 

1 

1 

2 

2 

2 

3 

.09 

1230 

1233  1236  1239 

1242 

12451247 

1250 

1253 

1256 

0 

1 

1 

1 

1 

2 

2 

2 

3 

.10 

1259 

1262  1265  1268 

1271 

12741276 

1279 

1282 

1285 

0 

1 

1 

l 

I 

2 

2 

2 

3 

.11 

1288 

1291129412971300 

1303  1306 

1309 

1312 

1315 

0 

1 

1 

1 

2 

2 

2 

2 

3 

,12 

1318 

1321  1324  1327  1330 

13341337 

1340 

1343 

1346 

0 

I 

1 

1 

2 

2 

2 

2 

3 

.13 

1349 

135213551358 

1361 

1365  1368 

1371 

1374 

1377 

0 

1 

1 

1 

2 

2 

2 

3  3 

.14 

1380 

1384 

1387 

1390 

1393 

13961400 

1403 

1406 

1409 

0 

I 

1 

1 

2 

2 

2 

3 

3 

.15 

1413 

141614191422 

1426 

1429  1432 

1435 

1439 

1442 

0 

1 

1 

1 

2 

2 

2 

3 

3 

.16 

1445 

1449145214551459 

1462.1466 

1469 

1472  1476 

0 

1 

1 

1 

2- 

2 

2 

3 

3 

.17 

1479 

14831486  14S9  1493 

14961500 

1503 

15071510 

0 

1 

1 

l 

2 

2 

2 

3 

3 

.18 

1514 

15171521  1524  152^ 

15311535 

1538 

1542  1545 

0 

1 

1 

1 

2 

2 

2 

3 

3 

.19 

1549 

1552  1556(  1560  1563 

1567 

1570 

1574 

1578 

15S1 

0 

1 

1 

1 

2 

2 

3 

3 

3 

.20 

1585 

1589  1592  1596  1600 

1603  1607 

1611 

1614 

1618 

0 

1 

1 

j 

^2 

2 

3 

3 

3 

.21 

1622  1626  1629  1633  1637 

1641  1644 

1648 

1652  1656 

0 

1 

I 

2 

2 

2 

3 

3 

3 

.22 

1660  1663  1667  1671  1675 

1679  1683 

1687 

1690  1694 

0 

1 

I 

2 

2 

2 

3 

3 

3 

.23 

1698 

1702170617101714 

17181722 

1726 

1730;  1734 

0 

1 

2 

2 

2 

3 

3 

.24 

1738 

1742174617501754 

1758 

1762 

1766 

1770  1774 

0 

1 

1 

2 

2 

2 

3 

3 

1 

.25 

1778 

178217861791 

1795 

1799 

1803 

1807 

1811 

1816 

0 

1 

1 

2 

2 

2 

3 

3 

.26 

1820 

1824182818321837 

1841 

1845 

1849 

1854  1858 

(J 

1 

1 

2 

2  3 

3 

3 

.27 

1862 

1866  1871  1875  1879 

1884 

1888 

1892 

1897  1901 

0 

1 

I 

2 

2  3 

3l3 

.28 

1905 

1910191419191923 

1928 

1932 

1936 

1941 

1945 

0 

1 

1 

2 

2 

3 

3 

4 

.29 

1950 

1954 

1959  1963  1968 

1972 

1977 

1982 

1986 

1991 

0 

1 

1 

2 

2 

3 

3 

4 

.30 

1995  2000 

2004  2009  2014 

2018 

2023 

2028 

2032  2037 

0 

1 

1 

2 

2 

3 

3 

4 

4 

.31 

204212046 

2051  2056  2061 

2065 

2070 

2075  2080 

2084 

0 

] 

1 

2 

2 

3 

3 

4 

4 

.32 

2089:2094 

2099^2104,2109 

2113 

2118 

2123 

2128 

2133 

0 

1 

1 

2 

2 

3 

3 

4 

4 

.33 
.34 

21382143 
2188  2193 

2148  2153 
2198  2203 

2158 
2208 

2163 
2213 

2168 
2218 

2173 
2223 

2178 
2228 

2183 
2234 

0 

1 

1 

1 

1 

2 

2 
2 

2 
3 

3 
3 

3 
4 

4 
4 

4 
5 

.35 

2239  2244 

2249 

2254  2259 

2265 

2270 

2275 

2280 

2286 

1 

1 

2 

2 

3|3 

4 

4 

5 

.36 

2291  2296 

2301 

23072312 

2317 

2323 

2328 

2333 

2339 

1 

1 

2 

2 

3'3 

4 

4 

5 

.37 

2344:2350 

2355  2360  2366 

2371 

2377 

2382 

2388 

2393 

1 

1 

2 

2 

3  3 

4 

4 

5 

.38 

2399  2404 

2410  2415  2421 

2427 

2432 

2438 

2443 

2449 

1 

1 

2 

2 

3  3 

4 

-: 

5 

.39 

2455  2460 

2466 

2472 

2477 

2483 

2489 

2495 

2500 

2506 

1 

1 

2 

2 

3  3 

4 

•> 

5 

.40 
.41 

2512  2518 
2570  2576 

2523 

2582 

2529 

2588 

2535 
2594 

2541 
2600 

2547 
2606 

2553 
2612 

2559 
2618 

2564 
2624 

1 
1 

1 
1 

2 
2 

2 
2 

3 
3 

4 
4 

4 
4 

5 
5 

5 
5 

.42 

2630,2636 

2642 

2649  2655 

2661 

2667 

2673 

2679 

2685 

1 

1 

2 

2 

3 

4 

4 

5 

6 

.43 

2692  2698 

2704 

2710  2716 

2723 

2729 

2735 

2742 

2748 

1 

1 

2 

3 

3 

4 

4 

5 

6 

.44 

2754  2761 

2767 

2773  2780 

2786 

2793 

2799 

2805 

2812 

1 

1 

2 

3 

3 

4 

4 

5 

6 

.45 

2818 

2825 

2831 

2838  2844 

2851 

2858 

2864 

2871 

2877 

1 

1 

2 

3 

3 

4 

5 

5 

6 

.46 

2884  2891 

2897 

29042911 

29172924 

2931 

293S 

2944 

1 

1 

2 

3 

3 

4 

5 

5 

6 

.47 

2951  1  2958 

2965  2972 

2979 

29852992 

2999 

3006 

3013 

1 

1 

2 

3 

3 

4 

5 

5 

6 

.48 

3020^027 

3034  3041  3048 

305513062 

3069 

3076 

3083 

1 

1 

2 

3 

4 

4 

5 

6 

6 

.49 

30903097310531123119 

31263133 

3141 

3148 

3155 

1 

1 

2 

3 

4 

4 

6 

G 

6 

I 

352 


TABLES. 


ANTILOGARITHMS. 


Logarithms. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

PROPOR 

9 

TIONAL  PARTS. 

123 

456789 

.50 
.51 
.52 
.53 
.54 

3162 
323€ 
3311 
3388 
3467 

-31703177 
>  3243  3251 
3319  3327 
3396  3404 
3475  3483 

31843192 
3258  3266 
3334  3342 
34123420 
3491  3499 

3199 
3273 
3350 
342* 

3508 

3206  3214 
3281  32*9 
3357  3365 
3436  3443 
3516  3524 

3221  322?  i    i 
32963304  i    2 
33733381  i   2 
34513459  l   2 
35323540  i   2 

3     44567 
3     45567 
3     45567 
45667 
45667 

.55 

.56 
.57 

.58 
.59 

3548 
3631 
3715 
3802 
3890 

3556  3565 
3639  364  S 
3724  3733 
138113819 
38993908 

3573  3511 
3556  3664 
3741  3750 
3828  3837 
39173926 

3539 
3673 
375^ 
3846 
3936 

35973606 
3681  3690 
37673776 
3855  3864 
3945  3°54 

36143622  i  2  2 
36983707  l   2  3 
37843793  123, 
38733882  1   2   3   - 
39633972  l   2  3  ^ 

45677 
45678 
45678 
45678 
55678 

.60 
.61 
.62 
.63 
.64 

3981 
4074 
4169 
4266 
4365 

3990 
4083 
4178 
4276 
4375 

3999 
4093 

4188 
4285 
4385 

4009  4018 
41024111 
4198  4207 
4295  4305 
4395  4406 

4027 
4121 
4217 
4315 
4416 

4036  4046 
41304140 
42274236 
4325  4335 
4426  4436 

4055  4064  128' 
41504159  1    2   3  ^ 
42464256  l   2  3  ^ 
4345^4355  l   2  3  ^ 
44464457  123* 

56678 
56789 
5    6789 
56789 
56789 

.65 
.66 
.67 
.68 
.69 

4467 
4571 
4677 
4786 
4898 

4477 
4581 
4688 
4797 
4909 

4487 
4592 
4699 
480S 
4920 

4498  450^ 
4603  4613 
47104721 
4819  4831 
49324943 

4519  4529 
4624  4634 
4732  4742 
4842  4853 
4955  4966 

4539  4550  4560  1234 
464546564667  1234 
4753  4764  4775  1234 

486448754887  1234 
497749895000  1   2  3  i 

567    89 
5    6   7    9  10 
57    8    9  10 
67    8    9  10 
67    8    910 

•70 
.71 
.72 
.73 
.74 

5012502350355047 
5129514051525164 
5248526052725284 
5370,5383:5395^408 
5495  5508  5521  5534 

5058 
5176 
5297 
5420 
5546 

5070 
5188 
5309 
5433 
5559 

6082 

5200 
5321 
5445 
5572 

509351055117  1   2  4  £ 
521252245236  l   2  4   5 
5333  5346  535S  i   2  4 
545854705483  1   3   4 
558555985610  1   3  4 

678    911 
6   7    8  1011 
67    9  1011 
6    8    9  10  11 
6    8    9  10  12 

.75 
.76 

.77 
.78 
.79 

5623 
5754 

5888 
6026 
6166 

5636 

5768 
5902 
6039 
6180 

5649  5662 
578  1!  5794 
5916|5929 
6053  6067 
6194  6209 

5675 
5S08 
5943 
6031 
6223 

5689 
5821 
5957 
6095 
6237 

5702 
5834 
5970 
6109 
6252 

571557285741  1345 
5848  5861  5875  1345 
598459986012  1345 
612461386152  1346 
6266  6281  6295  1346 

7    8    9  10  12 
7    8    9  11  12 
7    8    Cll  12 
7    8  10  11  13 
7    9  HV11  13 

.80 
.81 
.82 
.83 
.84 

6310 
6457 
6607 
6761 
6918 

6324 
6471 
6622 
6776 
6934 

6339  6353 
6486'6501 
66376653 
6792,6808 
6950  6966 

6368 
6516 
6668 
6823 
6982 

6383 
6531 
6683 
6839 
6998 

6397641264276442  1346 
6546  6561  '6577  6592  2356 
6699671467306745  2356 
6855687168876902  2356 
70157031^70477063  2356 

7    9  10  12  13 
8    9  11  12  14 
8    9  11  12  14 
8    9  11  13  14 
8  10  11  13  15 

.85 
.86 
.87 
.88 
.89 

7079 
7244 
7413 
7586 
7762 

7096 
7261 
7430 
7603 

7780 

7112 

7278 
7447 
7621 
7798 

7129 
7295 
7464 
7638 
7816 

7145 
7311 

7482 
7656 
7834 

7161 

7328 
7499 
7674 
7852 

7178 
7345 
7516 
7691 

7870 

71947211 
7362  7379 
7534  7551 

77097727 
78897907 

7228  2357 
7396  2357 
7568  2357 
7745  2457 
7925  2457 

8  10  12  13  15 
8  10  12  13  15 
9  10  12  14  16 
9  11  12  14  16 
9  11  13  14  16 

.90 
.91 
.92 
.93 
.94 

7943 
8128 
8318 
8511 
8710 

7962 
8147 
8337 
8531 
8730 

79SO 
8166 
8356 
8551 
8750 

7998 
8185 
8375 
8570 
8770 

8017 
8204 
8395 
8590 
8790 

035 
222 
414 
610 
810 

8054 
8241 
8433 
8630 
8831 

8072  8091 
8260,8279 
84538472 
8650  8670 

8851  8872 

8110  2467 
8299  2468 
8492  2468 
8690  2468 
8892  2468 

9  11  13  15  17 
9  11  13  15  17 
10  12  14  15  17 
10  12  14  16  18 
10  12  14  16  18 

.95 
.96 
.97 
.98 
.99 

8913 
9120 
9333 
J550 
9772 

8933 
9141 
9354 
9572 
9795 

8954 
9162 
9376 
9594 
9817 

8974  8995 
9183  9204 
939719419 
96169338 

9840  9863 

016 
226 
441 
661 

9886 

9036  9057  9078 
9247  920S  9290 
9462  94S4  9506 
M  is:  5  9705  9727 
9908  9931  9944 

9099  2468 
9311  2  4  6  8 
9528  2479 
9750  2479 
9977  2579 

10  12  15  17  19 
11  13  15  17  19 
11  13  15  17  20 
11  13  16  1820 
11  14  16  18  20 

INDEX. 


Alkalies  in  Boiler  Water,  Determination  of 308 

in  Silicates,  Determination  of 214,  217 

Aluminum,  Bonsai's  Method  for  Determination  of 23 

Decomposition  of  Ores  Containing,  by  HF  Treatment 20 

Direct  Method  for  Determination  of 20 

Indirect  Method  for  Determination  of 25 

in  Clays,  etc.,  Determination  of 25 

Ammeter,  Volt 10 

Ammonium  Acid  Sulphite,  Reagent 129 

Molybdate,  Standard  Solution  of 151 

Oxalate,  Reagent 67 

Thiocyanate,  Standard  Solution  of ' 48 

Antimony,  in  Ores,  etc.,  Determination  of 27 

in  Ores  and  Alloys,  Ro well's  Method  for  Determination  of.  .      34 
and  Tin  in  Babbitt  and  Type  Metal,  etc.,  Determination  of. .   333 

Separation  of  Arsenic  from 28 

Separation  of  Tin  from 30 

Apparatus i 

for  Hydrogen  Sulphide 4 

for  Standard  Solutions 6 

Arsenic,  Determination  of,  in  Ores 40 

by  Method  of  L.  L.  Krieckhaus 46 

by    Author's     Modification    of    Krieckhaus' 

Method 47 

by  Method  of  Ebaugh  and  Sprague 45 

by  Pearce's  Method,  Modified 42 

in  Lead,  Copper,  etc 41 

353 


354  INDEX. 

PAGE 

Arsenic,  Influence  of,  in  Copper  Determination 88 

in  Zinc  Determination 289 

Separation  of,  from  Antimony 28 

Ash  in  Coal  and  Coke,  Determination  of 320 

Available  Lime,  Determination  of,  in  Ores  Containing  Calcium  Fluoride.  70 

B 

Babbitt  Metal,  Determination  of  Antimony  and  Tin  in 333 

Barium  in  Ores,  Determination  of 49 

Short  Method  for  Determination  of 51 

Sulphate  in  Insoluble  Residue,  Determination  of 223 

Notes  on  Precipitation  of 243 

Battery  for  Electrolysis 10 

Solution 10 

Beaker  for  Electroylsis 1 1 

Bismuth  in  Ores,  etc.,  Determination  of 52 

by  Electrolytic  Method 54 

in  Lead  Bullion 57 

in  Refined  Lead 56 

by  Volumetric  Method 58 

Bismuthate  Method  for  Determination  of  Manganese 169 

Boiler  Water,  Ana\ysis  of 306 

Boiling  Rods 8 

Burette,  Funnel-Top 6 

Pinch-Cock  for. .  6 


C 

Cadmium  in  Ores,  Determination  of 61 

by  Electrolytic  Method 63 

Removal  of,  in  Zinc  Assay 292 

Sulphide,  Note  Regarding 298 

Calcium  Fluoride,  Approximate  Determination  of 71 

in  Limestone,  etc.,  Rapid  Volumetric  Determination  of 71 

in  Ores,  Determination  of 66 

in  Silicates,  etc.,  Determination  of 69 

Oxalate,  Separation  of  Magnesium  from 67 

Oxide  in  Boiler  Water,  Determination  of 308 

Carnotite,  Volumetric  Method  for 276 


INDEX. 


355 


PAGE 

Casseroles 2 

Cathode  of  Platinum  Wire  Gauze 14,  96 

Chlorine  in  Boiler  Water,  Determination  of 309 

Mohr's  Volumetric  Method  for  Determination  of 75 

Chromate  Method  for  Determination  of  Lead 144 

Chromic  Acid,  Determination  of 78 

Solution  for  Phosphorus  Determination 209 

Chromium  in  Chrome  Iron  Ore,  Determination  of . 78 

Chrome-  and  Chrome-Nickel  Steel,  Determination  of 82 

in  Iron  Ores,  Determination  of  Small  Amounts  of 77 

in  Steel,  Determination  of 81 

Clay,  Alkalies  in,  Determination  of : 214,  217 

Aluminum  in,  Determination  of 25 

Iron  in,  Determination  of '. .  .    127,  138 

Silica  in,  Determination  of 225 

Coal  and  Coke,  Analysis  of . 318 

Coal,  Heating  Value  of 326 

Cobalt  in  Ores,  Determination  of 188 

by  Electrolytic  Method 193,  203 

Sensitive  Test  for 197 

Separation  of,  from  Nickel 192,  194,  195,  198 

Coking  Quality  of  Coal,  Determination  of 321 

Combining  Determinations: 

Calcium  and  Magnesium 304 

Copper  and  Iron 305 

Copper,  Lead  and  Insoluble > 303 

Insoluble,  Iron,  Calcium,  and  Magnesium 304 

Insoluble,  Lead,  Copper,  and  Iron 305 

Zinc,  Iron,  and  Insoluble 304 

Conducting  an  Electrolysis 13 

Cooling  Box 4 

Copper,  in  Ores,  Determination  of,  by  Colorimetric  Method 107 

by  Cyanide  Method 97 

by  Electrolytic  Method. . .   91,  95,  96,  106 

by  Iodide  Method 86 

by  Permanganate  Method 102 

Rapid  Determination  of t 90 

Current  Density 13 


556  INDEX. 


D 

PAGE 

Bichromate  Method  for  Iron  Determination 132 

Distillation  Test,  Engler's,  for  Crude  Petroleum •  „•  •  •    330 


E 

Electrode,  Rotating 14 

Electrodes 1 1 

Electrode  Tension 14 

Electrolysis 10 

F 

Filtration  of  Gelatinous  Precipitates,  Rapid  Method  for 7 

Fire  Assay  Button,  Determination  of  Lead  in 153 

Fixed  Carbon  in  Coal  and  Coke,  Determination  of 321 

Flasks,  "Copper" i 

Erlenmeyer a 

Flask-Holder ';  ^ 

Fluorine,  in  Ores  and  Slags,  Determination  of 113 

in  Fluorspar,  Volumetric  Method  for  Determination  of 115 

Folin,  Notes  on  the  Precipitation  of  Barium  Sulphate 243 

Funnels a 

Funnel-Support 3 

G 

Glass,  Measuring 5 

Guess,  Electrolytic  Method  for  Determination  of  Copper 95 

Permanganate  Method  for  Determination  of  Copper 102 

H 

Handy,  Volumetric  Method  for  Determination  of  Magnesium 159 

Hard  Lead,  Determination  of  Antimony  in 33 

Hillebrand,  Dr.  W.  F.,  Errors  in  Silica  Determination 232 

Holder,  Flask ,  4 

Hydrogen  Sulphide  Apparatus 4 

Waring's 296 


INDEX.  357 


PAGE 


Insoluble  Residue  in  Ores,  etc.,  Determination  of 231,  234 

in  Substances  that  Gelatinize  with  Acids,  Determina- 
tion of 224 

Methods  of  Am.  Sm.  &  Ref.  Co.  for  Determination  of.    234 

Iodide  Method  for  Copper  Determination 84 

Iron,  Determination  of  by  Dichromate  Method 132 

by  Permanganate  Method 119 

by  Zimmermann-Reinhardt  Method 130 

in  Boiler  Water 307 

in  Chrome  Iron  Ore 130 

in  Ores 125,  131,  136 

in  Refractory  Oxides,  etc 128,  138 

in  Silicates,  etc 127,  138 

in  Titaniferous  Ores 129 

Metallic,  for  Standardization 120 

Standard  Methods  for  Analysis  of 138 

Ores,  Determination  of  Chromium  in 77,  78 

Phosphorus  in 206 

Titanium  in 260,  264 


j 

Jannasch,  Method  for  Decomposition  of  Silicates 230 


K 

Kneeland,  Method  for  Determination  of  Fluorine 113 

Krieckhaus,  Volumetric  Method  for  Determination  of  Mercury 181 


L 

Lead  Bullion,  Bismuth  in,  Determination  of 57 

Lead,  Determination  of,  by  Alexander's  Method,  Modified 149 

by  Chromate  Method 144 

in  Fire  Assay  Button 153 

in  Roasted  Products 153 

Short  Method  for 152 


358  INDEX. 

PAGB 

Lead,  Refined,  Determination  of  Bismuth  in 56 

Sulphate  in  Ores  Containing  Barium,  Extraction  of 148 

Titration,  Standard  Ammonium  Molybdate  Solution  for 151 

Limestone,  Determination  of  Magnesium  in 158 

Phosphorus  in 211 

Logarithms 16 


M 

Magnesium  Ammonium  Phosphate,  Neubauer's  Method  of  Precipitating  157 

Magnesium,  Determination  of,  Handy's  Volumetric  Method  for i^g 

in  Limestones,  Silicates,  etc 158 

in  Ores,  etc 155 

Magnesia  Mixture,  Reagent 213 

Magnesium  Oxide  in  Boiler  Water,  Determination  of 308 

Manganese,  Determination  of,  by  Bismuthate  Method 169 

in  Ferro -Manganese 173 

in  Ferro-Silicon 1 73 

in  Iron  Ores 1 72 

in  Ores 162,  167 

in  Pig  Iron 1 72 

"    in  Special  Steels. 1 73 

in  Steels 170 

Manganese  Sulphate,  Reagent 131 

Measuring  Glass 5 

Mercury -Ammonium  Carbonate,  Reagent 229 

Mercury  in  Ores,  Determination  of,  by  Dry  Method 18® 

by  Eschka's  Method 181 

by  Krieckhaus'  Volumetric  Method.  181 

by  Seamon's  Volumetric  Method. .  . .  183 

by  Wet  Method 1 79 

Miller  and  Frank,  Volumetric  Determination  of  Bismuth 58 

Moisture  in  Coal  and  Coke,  Determination  of 318 

Molybdenum  in  Ores,  Determination  of 185 

Qualitative  Test  for 187 

Molybdic  Acid,  Note  Regarding 211 

Solution  for  Phosphorus  Determination 209 


INDEX. 


N 


359 


Nickel,  Determination  of,  by  Electrolytic  Method 193,  203 

by  Volumetric  Method 199 

in  Nickel  Steel 201 

in  Ores 188 

in  Steel 198 

Separation  of  Cobalt  from 192,  194,  195,  198 

No  yes,  Colorimetric  Method  for  Titanium  in  Iron  Ores 264 

O 

Organic  and  Volatile  Matter  in  Boiler  Water,  Determination  of 306 

Oxalic  Acid,  Standard  Solution  of,  for  Manganese  Determination 166 

P 

Parry,  Method  for  Assay  of  Tin  Ore 252 

Pearce's  Method,  Modified,  for  Determination  of  Arsenic 42 

Pearce's  (E.  V.)  Method  for  Assay  of  Tin  Ores 250 

Pencil  for  Glass 8 

Penfield,  Volumetric  Method  for  Determination  of  Fluorine  in  Fluorspar.  115 

Permanganate  Method  for  Determination  of  Iron 119 

Petroleum,  Engler's  Distillation  Method  for  Testing  Crude. 330 

Phosphorus,  Determination  of,  by  Volumetric  Method 209 

in  Coal  and  Coke 324 

in  Iron  Ores 206 

in  Limestone 211 

in  Pig  Iron 139,  208 

•                         in  Steel 208 

Pinch-Cock  for  Burette 6 

Potassium  Bromate,  Standard  Solution  of,  for  Antimony  Determination  .  .  35 

Cyanide,  Standard  Solution  of,  for  Copper  Determination 98 

Dichromate,  Standard  Solution  of,  for  Iron  Determination 133 

in  Silicates,  Determination  of 214,  217 

Iodide,  Reagent 89 

Permanganate,  Standard  Solution  of,  for  Iron  Determination.  119 
Permanganate,  Standard  Solution  of,  for  Calcium  Determina- 
tion    68 

Separation  of,  from  Sodium 218 

by  Indirect  Method 220 


360  INDEX. 


R 

PAGE 

Refined  Lead,  Determination  of  Bismuth  in 56 

Rotating  Electrode 14 

Rowell's  Method  for  Determination  of  Antimony 34 


S 

Seeman,  Method  for  Determination  of  Silica  in  Ores  Containing  Fluorine.   229 

Silica,  Determination  of,  Accurate  Method  for  the 232 

as  Insoluble  Residue 221,  234 

Common  Errors  in  the 232 

in  Boiler  Water 307 

in  Ores  Containing  Fluoride 229 

in  Substances  that  Gelatinize  with  Acids 224 

Seeman's   Method   for   Determination   of,    in    Ores    Containing 

Fluorine 229 

Testing  the  Purity  of 228 

True,  or  "Silica  by  Fusion" 225 

Silicates,  Alkalies  in,  Determination  of 214,  217 

Decomposition  of,  by  Hydrofluoric  Acid 127 

by  Lead  Oxide 230 

Silver  Nitrate,  Decinormal  Solution  of 76 

Reagent  in  Arsenic  Determination , 43 

Smith,  J.  Lawrence,  Method  for  the  Determination  of  Alkalies  in  Sili- 
cates    214 

Sodium  Ammonium  Phosphate,  Reagent 156 

in  Silicates,  Determination  of 214,  217 

Separation  of,  from  Potassium 218 

by  Indirect  Method 220 

Thiosulphate,  Standard  Solution  of,  for  Copper  Determination. .     84 

Solids,  Total,  in  Boiled  Water,  Determination  of 306 

Solution  for  Battery 10 

Specific  Gravity  of  Coal  and  Coke,  Determination  of 325 

of  Crude  Petroleum,  Determination  of 329 

Standard  Solutions,  Apparatus  for 6 

Stannous  Chloride,  Reagent 130,  132,  182 

Starch  Solution,  Preparation  of,  for  Indicator 86 

Steel,  Chromium  in,  Determination  of 81 

Phosphorus  in,  Determination  of 208 


INDEX.  361 

PAGE 

Sulphur,  Determination  of,  in  Coal  and  Coke 322 

in  Ores 238 

in  Ores  Containing  Barium  Sulphate  . . .   238,  240 

in  Ores,  by  Waring's  Method 241 

in  Roasted  Ores,  or  Ores  Containing  much 

Copper 242 

in  Liquid  Fuel 244 

Method  of  Ebaugh  and  Sprague  for 238 

Sulphur  Trioxide  in  Boiler  Water,  Determination  of 308 

Support,  Funnel 3 

Supports  for  Electrodes  and  Beaker n 

Surface  of  Work-Table. . ,  6 


T 

Tables 341 

Antilogarithms 351 

Atomic  Weights 344,  345 

Chemical  Factors  and  their  Logarithms 346 

Conversion  of  Thermometric  Readings 343 

Conversion  of  Milligrams  per  Kilogram  to  Grains  per  Gallon 316 

Factors  for  Use  in  Water  Analysis 31 7 

Tables: 

Logarithms 349 

Measures  and  Weights 342 

Relation  of  Baume  Degrees  to  Specific  Gravity 341 

Tension,  Electrode 14 

Tin  in  Ores,  Determination  of,  by  Method  of  E.  V.  Pearce 250 

by  Method  of  E.  V.  Pearce,  Modified. . .   246 

by  Parry's  Method 252 

Titanic  Oxide,  Standard  Solution  of 266 

Titanium  in  Iron  Ores,  Determination  of 260,  264 

in  Pig  Iron,  etc.,  Determination  of 264 

Source  of  Error  in  Phosphorus  Determination 207 

Tungsten  in  Low  Grade  Ores,  Determination  of 270,  271 

in  Wolframtie  and  Oxidized  Ores,  Determination  of 267,  268 

Uranium  in  Ores,  Determination  of 273,  275,  276 

Separation  of  from  Vanadium 273,  275,  276 

Volumetric  Method  for  Determination  of,  in  Carnotite 276 


362  INDEX, 


V 

PAGE 

Vanadium  in  Ores,  Determination  of 277,  279,  281 

Separation  of,  from  Uranium 273,  275,  276 

Volatile  Matter  in  Coal  and  Coke,  Determination  of 319 

Error  in  Determination  of 323 

Volhard's  Volumetric  Method  for  Silver 43 

Volt-Ammeter 10 


W 

Waring  Method,  Modified,  for  Zinc  Determination 299 

Waring,  Method  for  Sulphur  Determination 241 

Method  for  Zinc  Determination 294 

Wash-Bottle  for  Ammonia,  etc 8 

Water,  Boiler,  Analysis  of.     See  Boiler  Water. 

Wohler,  Method  for  Aluminum  t)etennination. 22 

Work-Table,  Surface  of 6 


Z 

Zimmermann-Reinhard  Method  for  Iron  Determination 130 

Zinc,  Determination  of,  as  Pyrophosphate 301 

by  Low's  Method 284,  290 

by  Waring's  Method 294 

Modified 290 

in  Low  Grade  Zinc  Ores,  Slags,  etc 298 

in  Ores 284,  290,  291,  294,  299 

Modification  to  Remove  Cadmium  in  Determination  of 292 

Oxide  Emulsion,  Reagent 163 

Reagent 121 


-1 


ri 

£>: 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 


Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 

fc  j  i  fc 

nTTT 

APR     3  1955 


LD  21-100m-ll,'49(B7146sl6)476 


438545 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


